religion/cultural respect/ethics question

I teach the "most disabled" class of students at my school (I really need to get a better way of describing it, but basically life skills for significantly disabled students). All of my students are either first generation or immigrants from very diverse cultures (Guatemala, Somalia etc. there is no trend). I have one student who is Muslim and wears a Hijab. Sometimes she likes to take it off. I teach at a public school and I'm obviously not the religious police. If I was a gen ed teacher I'd say nothing. But as a special ed teacher one of my jobs is teaching the kids to cover up appropriately, keep their clothes on etc. In my culture we don't care about if our hair is covered so a Hijab is not expected but it is HER culture, but because culture and religion are so mixed together here it's complicated. Should I be encouraging her to keep it on? I guess the question is, is this more an issue of respecting her culture or maintaining 1st amendment freedoms?

edit: So far I've had a hands off policy, basically it's an issue of religion so I'm not touching it.