I think it might be more of just letting loose at home because she can't or doesn't think she can do so at the preschool.
Even if she 'could' let loose at school, the social cost would be super high. The cost was high on my son, and he had the 'boys will be boys' defense to fall back on (talk about tangled gender things) but girls who step out of line at school are opening themselves up for some high costs. Some do anyway, but the ones who are high EQ enough to dodge it, often will save it up for home. There are lots of references to gifted kids being more androgenous than ND kids. Who knows if it's even true. But if it is, my thought is that it's the kind of androgenous where they have LOTS of qualities that match their gender expectations and rather a lot of qualities that don't match, instead of being 'half way in the middle' or 'rather neither' although amoung us here I'll bet we could find plenty of kids in every catagory.
I love that when you slow down things go better, and I hope that the products work for you. I was thinking that maybe you could keep a picture of her bun for her to hold while you do her hair so she could keep her eyes on the goal.
Maybe a good compromise is bangs to eliminate the barrettes, while keeping the back hair long for the bun?
Love and More Love,
Grinity