Need Help with Angry/defiant 2 1/2 Year Old

I wouldn't wait to do something either. You don't want your child to develop these bad social habits. I would suggest reading the book by Jim Fay called Parenting with Love and Logic. It is a great resource that really helps in these kind of situations. While your daughter may not understand why she is behaving this way, it sounds like she is able to understand directions. This book is all about offering choices to give the child some ownership in their own life. You decide the choices that are ok with you and she gets to choose. This way you have set boundaries that are acceptable no matter which choice she makes. (example "would you like to to play with your toy or watch a movie while I feed the baby?")
You could even talk to her about what it should look like/sound like when you are attending to her brother or putting her to bed. See if she can tell you in her own words. This will let you know if she truly can follow directions or not.
Set up some kind of reward system (i.e. sticker chart/behavior chart- you can check at local teacher stores for these kind of things)When she does something correctly reward and praise her for it. Do this often at first (after each positive thing she does and then after she follows a couple directions correctly, etc.) Also make sure when praising her to connect it to an intrinsic motivator such as "I really liked the way you watched your movie while I fed baby brother. You are such a good helper for mom. Doesn't that make you feel good inside?"
This way she will start to want to please you instead of getting a sticker, reward etc.
If she doesn't follow through with your direction or choice she made, then you will need to set up some sort of consequence such as time out. At her young age, she shouldn't be in time out for more than a few minutes. Set the kitchen timer and then ask if she is ready to play nice again. Make sure you tell her what it was that she did wrong. This is the hardest part. You have to be very consistent with your actions so she knows you mean business.

I would also plan to do something special with her (just the two of you and your husband should spend some one on one time with her as well) several times a week if not daily. It sounds like she is acting out for attention, so you need to focus on giving her some alone time, but not at the expense of turning into a holy terror for you.

I also highly recommend the show Nanny 911. They provide a lot of good strategies to set up structured routines that are fair and easy for kids to understand.

Good luck to you! I am expecting a daughter in May and my son will be right at 18 months old. I may be in the same boat! Ugg!!

HTH,
A.

We have a 2 1/2 year old little girl right now too, she has an older brother not a little brother but I can relate to similar behavior. My husband and I also didn't know where to turn, my sister in law suggested a book called Love and Logic Magic for Early Childhood:Practical Parenting from Birth to Six Years by Jim Fay. It is an amazing book and truly has turned our household from stressful to fun. It sounds cheesy and I wasn't a 100% believer at first but I started using the suggestions that the book gave and it works it really works. Just like anything do what is best for your situation & good luck!

It sounds like you have tried quite a few things. I know she is little but she knows what she is doing is wrong. I would sit down with her (with your husband) and explain of the things she has been doing wrong and tell her why they aren't ok. then i would explain to her what will happen if she keeps doing these naughty things. (sit down with your husband before hand to work out a set disciple for these offenses) But while you are setting the consequences of her actions set good things that can happen too. Examples - if she plays nice while mommy feeds the baby then mommy will color with her for 10 minutes, if she doesn't then she has to sit in a time out.

I know that angry kids can be hard to deal with, our oldest son actually went to a psychologist between the ages of 3-4 to help deal with some issues and anger was one of them. According to our doctor it is ok to force a child to sit in time out. He had us sit our son in a chair for time out and place our hands either on his legs or arms and if he resisted we would force him to sit, while calmly explaining to him that he was going to sit until mommy/daddy told him he could get up. If she is really fighting you, hold her on your lap and make her stay there until she calms down. The key is to have her sit until she calms down, not for a set time limit. Then when the time out is done, make sure you explain to her why she sat in time out and then thank her for sitting (even if it was forced).
I know this sounds harsh but it worked wonders for our son. The key is to teach them to control their temper, don't get me wrong he still has some issues with it but not nearly as many or as bad, and when he started having problems throwing fits we still go back to this method.