Does the class space have lots of sensory input? bright colors, flourescent lights, muisc, clapping, shouting, "organized" chaos? you get the picture.
If so, maybe the music is the final straw that broke the camel's back? My dd(7) went to gymnastics at that age and we had a similar experience. dd loved the activities, but if it was overly stimulating for her, she would come unglued.
We ended up leavng lessons behind. If it isn't fun for her then it is not worth it.
We swim now and it is so much better.
