3yo behaviour

[Tanito279]

I'll start by saying that nursery have no concerns. I posted about a year ago about DD who finds it impossible to concentrate in a group setting (ballet and gymnastics). The advice was to have some time off and then try again. So she had 6m off and then I thought I'd try again - mainly because I want to meet other parents, arrange play dates etc. There has been little improvement in the classes. She requires 1:1 attention or she doesn't listen, wanders off, generally won't comply. Sometimes she will let a teacher guide her, others she'll scream if touched and run away laughing. I know that I'm going to have to take her out of the classes, but I'd really like her to go. I've made friends, she's made friends, she talks about the class, the teacher and her friends all week. Then we get to the room and Boom.
In a class of 20-25 children and 3 adults, why is she the only one? Yes she drinks squash. She has no tv before 3pm. She doesn't eat chocolate but has occasional sweets. Single parent and only child.
For what it's worth, she also hates being in any room on her own which is slowly driving me crazy. She doesn't have tantrums and sleeps for 12 hours a night.
This is long and garbled, sorry.