Your post sounded to me that your MIL takes over during the party. I think having a friend there to support you is a good idea. The friend can "coach" you if you'd like and plan for that but she/he shouldn't try to rescue you.
Will this party include adults? Perhaps you could have a children only party and then another combined one for your mil and daughter's birthday.
I'd like to tell you about my experience as a mil. During the first few years after the birth of my first grandchild my daughter felt that I took took over. decisions. It was very confusing to me because she was angry when I didn't do those things. It was a boundary issue. I suspect that she was having difficulty setting boundaries in part because she wanted me to do most of the housekeeping but at the same time she was angry about it.
It's been 4 years since I stopped staying at her house during the day after she told me she would take her children to child care. I was hurt and expressed that hurt with anger. I wanted her to learn to accept my help. Starting then we have both learned more about what boundaries we want and how to let the other person know our boundaries in tactful ways. Peg's message expresses the issue of boundaries and making the party yours.
You won't be able to always be calm and rational at first. How quickly this strategy works depends on both you and your mil. Have you been able to be friends with her? Do you understand why she does this? Does she take over in other places than the party? Is the party the main/only time that you're upset? Is there any part of your mil that you like?
My daughter and I got along so much better when we were able to tell each other how we felt and each of us accept the other's feelings even when we didn't think they "should" feel that way. I finally learned to do this by listening without making comments. Just listening is difficult especially when I felt that a part of what she said was critical of me. A recent article I read described this as listening but not hearing.
I had to learn to detach myself from the conversation. To do that I have to be aware of the words that start the anger cycle. Then I say to myself or my daughter says to me, "These are her/my feelings. Don't take it personally."
Definitely easier said than done. So don't allow yourself to discouraged enough to stop being assertive. I did find that when I had a good friend with me that I was better able to manage my feelings.
Your mil may not be able to share feelings or accept feelings. I've had that experience too. If that's the case then it's beneficial for you to learn ways to resolve your own anger, mistrust, frustration, etc. A part of doing that for me is to know what I want, recognize how I'm feeling and talk myself out of being angry or into being detached.
Setting your boundaries; i.e; knowing what you want before the event is absolutely necessary. If it helps write everything down. How you let your mil what your boundaries are concerning the way she acts (or not) depends on your and your mother's personalities and relationship. If you can feel empathy for your mil you will feel less frustrated and angry and be better able to make what you want to happen, happen. If you can focus on your own needs while recognizing your mil's importance to your family the conversation will go better. Perhaps she "takes charge" so that she will feel important.
Perhaps your mil has always been the take charge sort of person. If she's the oldest of her sibs, it's likely that she is. You can also get a clue about her need to be in charge by looking at her work history. If she had a job that required her to take charge and was successful at it she will still be taking charge. If she was a sah mom without a husband or with a husband who wanted/let her take charge she is still doing that. She cannot and will not stop being a "take charge" woman.
The way you work with a "take charge" person is to put them in charge of something that they will feel is important. My daughter tells me the theme for the party and asks me to find games. I tell her what I've found, usually by e-mail, and she tells me which ones she wants. I put together what props are needed and how to implement the game. Then, sometimes I am in charge of playing the games with the children while she puts together the cake, gifts, etc. A couple of times we did the games with the kids together. Once I didn't go to the party (my choice because we were fighting and I stuck with my boundary-very painful). She called her father who helped her.
That is the only time he's gone to a party. That's his boundary and his lack of attendance is about his issues and not my daughter's. It has taken both of us years to be able to accept her father's on and off relationship with her.
Acceptance is the key to getting along and it does take some of us longer than others to be able to do that. The first thing I had to learn was how I felt and what I could do to change how I felt. Setting and remembering boundaries was the next step. I still, sometimes, have to write them down. For example: I just automatically do whatever I see that needs doing. I often felt resentful that my daughter didn't appreciate my help but I still did the chore.
She asked me not to do chores for her unless she asked me for help. We made the same agreement about giving advice. At first I thought that it was my job to help my daughter who did/does need my help, in my view. I was still feeling and acting like a mother. My daughter thought she couldn't tell me not to do what I was doing because she was still a daughter. Both of us were frustrated and angry. We had many verbal fights on our way of understanding ourselves and the dynamics of our relationship.
Your mil may think she's helping you. She won't know differently until you let her know by telling her in a kind way what your have plans are for the party and what she can do to help. Above all do not say that you don't need her help.
Or you can tell her that you appreciate her help but you want to try doing this party with just the kids and the parents (or whatever combination you want). However you say it, it will be most likely to work if you can express how you feel about doing the party without telling how you feel about her involvement in the party. It's likely that she will insist that she wants to help. Acknowledge her offer by letting her know that you appreciate her willingness but this is what you need to do for yourself. That sort of thing. Use "I" sentences. For example: "this is what I am going to do."
Realize that she may insist that she be involved and put the pressure on you. Just keep repeating "this is what I'm going to do." Be prepared for her to feel hurt, angry, use "poor me" language, etc.
I was confused for many years about the difference between thinking of myself doing what I want and thinking of the other person while doing what I want. I felt that if I did what I want and I hurt the other person's feelings that was not OK. I felt that it was my responsibility to make everyone around me happy even when it made me unhappy.
I learned that how other people feel is not my responsibility. If they're happy, very good. If they're angry, too bad. I'll probably be sad that they're angry and may be angry that they don't accept what I'm doing.
I thought, and still do more often than I like, that I should do what I think the other person wants me to do or let them do what they want to do. When I was trying to make the other person happy, I was angry. The other person most likely "knew" that I was angry from the way I spoke and acted. Ultimately no one was happy. When what we were doing involved other people everyone became tense.
How do I stop feeling angry? By being true to myself, having boundaries, and enforcing them. I cannot change how the other person feels. Sometimes they didn't like the situation either but we seldom talked about what each of us wanted.
Try to give your mil "the benefit of the doubt." I have frequently been in both your position and your mil's position. In your position I would feel as you do; that she took over and I was angry. In your mil position I would feel your tension and tentativeness and think, she needs my help. I would be doing this out of my perception of what you needed and providing that for you.
I am aware that your mil may not be that aware or have that attitude. She may take over in an angry way. She may sense, perhaps unconsciously, that you are wishy-washy and don't have a good plan. Because you don't stand up for yourself and manage the party, she takes over and feels angry that the party is not going Ok in her estimate. There may be other reasons for her action. Whatever her reasons, she's able to take over because you let her. Also no one can make us angry without our permission. Another "easier said than done" sort of situation. No one can make us angry feels wrong. They did this which made me angry. However, each of us has the choice to be angry or not once we learn to manage our feelings.
In summary:
" I am woman! I am invincible!" That's from a song that was popular during my younger years.
Plan the party with your husband and daughter, asking mil for suggestions. Know what you want, but be willing to make some compromises. You decide what you can compromise.
Be as diplomatic as possible as you plan and execute your plan. Make "I"
statements. "This is the way I am going to do this." Only ask for suggestions in areas that you are willing to compromise on or haven't decided on.
Remember that she will always be a part of your family and do as much damage control as you can.
Know that this won't be easy. You will get better with practice so tell yourself, "I'm OK. I'm learning." I found that, at first, I felt guilty, sometimes frightened, and helpless. I said, "I'm sorry" too often. I eventually accepted that I didn't have enough practice yet and expected and planned for the other person having hurt feelings, anger, or whatever feeling.
At the party you take charge from the very beginning. Know what you want and how to make it happen. If anyone tries to take over calmly redirct them and the party towards your plan. I learned a version of this phrase from another Mamasource mom. "Thank you for helping AND my plan is ......." Using the word "and" sounds and feels less judgemental. You could also eliminate the "and" and make your statement 2 sentences.
If/when your mil gets difficult repeat to yourself, "I'm not responsible for how she feels or "I am woman! I am invincible!" Say to yourself and/or your friend whatever works to bolster your courage. Plan out how your friend can support you, without facing the mil, ahead of time.
The answer to your question is so complicated it is difficult to make it short. Peg and Laura answered it well!
I'm wishing that your party be a happy one.
