I wonder if perhaps some of what is going on here is your possibly a little over anxious and worrying too much, having had an NICU baby who still suffers with a lot of viruses and hospital trips. I'm just completely speculating here not knowing you at all but perhaps you are a little hyper aware of the reaction of members of the public to your child, perhaps you are hyper aware of her sometimes different behaviour because perhaps you are worried about her fitting in and being normal and not falling behind compared to non NICU babies?
2 year olds can be absolutely mental, members of the public can either be completely rude or wonderfully kind and everything in-between, the odd stare is normal, sometimes we are having a bad day or we're in a mood and seeing a grumpy or wild toddler is just irritating and we forget to be kind.
I'm also flabbergasted there are ballet and gymnastic classes for 2 year olds! It was all church hall parent and baby groups, soft play dates and swimming sessions in the baby pool (so no need for parents to be able to swim) when mine were that age. The thought of trying to get mine to behave in a proper dance class is mental, my eldest was still shitting his pants and not speaking at aged 2 (he's a totally normal, functioning, very articulate, well behaved 13 year old now).
I'd say, take a step back, forget ballet for a year or two, breathe, both of you try and relax, enjoy the already sometimes over-stimulating festive period doing less structured stuff and try and just have relaxed, free (in both ways) fun together.