First, I applaud your courage for reaching out on this. It's such an emotional thing.
Hitting a parent means the child does not respect you, for whatever reason. This is Child development, 101. It could be temporary, it could be longer-lasting. Either way, she knows that hitting is not ok, and is doing it because she is upset. It does NOT mean that she does not love you, or care for you, etc. It DOES mean that she is hurting in some way.
The important thing is to address it calmly but firmly, explaining that we do not hit, that it is not ok. Tell her that it hurts mommy (but don't go as far as making her kiss it. That's a bit silly.) Tell her that you love her very much and that you know she is a wonderful girl who is capable of not hitting.
Setting clear boundaries in a calm, non-dramtic way is one way that children learn to respect us. It says, "I am the mommy, and I am teaching you what is ok and not ok because I love you so much."
The worst thing you can do is punish her by putting her in a time out. Children at this age do not understand a timeout. They interpret it as being "sent away" or isolated, which of course, it is. It is punitive, meant to "punish" bad behavior.
Your daughter hitting you is not deliberately trying to hurt you (bad behavior). She just does not have the vocabulary to express how she is feeling, and is also dealing with rising hormones in her little body. All of this is pretty tough on a little kid. I know it's also tough on us moms (my son tries me all the time), but the best thing we can do for them is to extend our compassion ("mommy knows you are frustrated (sad / upset) and I'm sorry about that. And I also want you to know that it's not ok to hit mommy."
Acknowledging our children's feelings --without labeling them as good/bad -- is one of the MOST important things we can do to develop their healthy self-esteem. It sends them the message loud and clear that their feelings are real, acknowledged and allowed. In the absence of this acknowledgement, children grow up thinking it's not ok to be frustrated, or angry, or even resentful, so they bottle them up and let loose later in life.
I am not an expert, but I have read and talked to experts on this subject. My longest standing friend of 17 years is a renowned Montessori Teacher Trainer, and has been in the world of child development for over 25 years. I have been fortunate to receive lots of great input from her on child development stuff.
She runs a well-nown Montessori school for children from age 3 to grade 6 - with over 200 students. They have recently incorporated positive discipline vs. timeouts - for all ages.
One last note, I was recently touring private preschools in the SFV and one of the teachers wanted to convert her 2 and 1/2 year-old classroom to positive discipline. She started by having the children come up with the list of "ok" and "not ok" choices, explaining that they always had a choice of which behavior to use. An astonishing thing happened: the children had no trouble creating a long list of "not ok" behaviors but had difficulty coming up with even a few ok behaviors. What this tells us is that by age 2 and 1/2, the feedback most children get from their parents / caregivers is mostly about what they are doing wrong (not ok choices), rather than reinforcing what they are doing right. It certainly opened my eyes! Yikes! Gotta do more positive feedback in our house!
I wish you all the best as you sort this out. And having used the services of the Regional Center myself, it might be a good idea to have an early intake to screen out any developmental issues.