C.S.
I work for a Court in Ca. I can't really tell you what to prepare for, though I have one piece of advise to offer. Find a sitter for your daughter while you are at the appointment. If you havent got anyone you can trust check with your local Court to see if they offer a children's waiting room. It is of the utmost importance that your child NOT attend mediation with you, for countless reason but I will caution you on 2:
1. You need to feel free to speak your piece and there is no way you could or should do that in front of your child.
2. Even though your child is young, she will be affected by what happens in mediation. She should not be present.
Best of luck to you. I pray for a reconsiliation if that is in your heart and guidence for you if you chose to divorce.