Thank you so much for the posts. I feel like I was on the right track in trying to expose her early to a variety of activities so she would feel compelled someday to chose something she loves. Perhaps in doing so my husband and I pushed her into doing something she wasn't quite ready for - although it has been a bit frustrating that the other children seem to adore this activity and ours was the sole child who didn't respond accordingly. It did seem that the more we pushed and took away privileges when OUR expectations were not met by her behavior, the worse she got.
Upon reflection, this may be a control thing on her part. We will focus on her ballet (without making too big of a deal on her participation in it) instead since she seems to enjoy this more and hope she will want to return to gymnastics at some point. While I don't expect her to ever compete in the sport -- I just want her to have all the doors open she can in terms of choosing future sports and these early classes do, I believe, help to lay a foundation.
My son is very similiar. One session he will love music - the next time - not! Nine months ago he refused to play soccer and walked off the field crying - now he is ahead of the others and enjoys ever minute. One thing that I have found that works best for him are smaller groups of 5 or so. Saturday classes seem always larger (in the area we live and the activities we particpate in) and usually the facility as well is very busy (and loud)! I have noticed that in these situations - and others like this, he seems to be frightened. I now always try to find a class with a small number of children and that (for us) has made a big difference. Good luck!
Four years of age is quite young for group sports. If she does not particpate, then let her watch from the sidelines - sometimes it takes time for a child to want to be part of a larger group. This really is not a "big" deal in the scheme of things and punishing her for "not participating" (which I believe she might not be mature enough to handle) probably won't solve the issue. However, time and patience probably will. Just my two cents worth ....