Should my grand daughter be allowed to hide behind her hair at a school?

My grand daughter is 4, and started pre-school this year. Mom always puts her hair in a pony tail because the teachers told her that my grand daughter hides behind her hair in school. If Mom doesn’t put it in a pony tail, the teachers will.
I’m very ambivalent about this. If it makes her feel more comfortable to “hide” then why not let her, until she’s ready to come out on her own? The problem is, I don’t know how she acts when she does it. Does she drop out altogether? Does she quit paying attention? If so, that’s a problem. But if she’s still participating, and answers questions and not being disruptive, I think she should be allowed to hide if she wants.

What are your thoughts?

As a side note, yesterday I asked my grand daughter why she hides behind her hair at school. She took it literally and said, “Gramma! I can’t hide “behind” my hair!! It’s on my head!” Well, duh, Gramma!