I would just let this person pick their own costume - she will know best what she will be comfortable wearing.
She can pick pretty much anything. If she wants to pick a character with a similar skin tone, okay ! If not, okay ! A hijab or such can be worked into pretty much any costume - and alterations can be made to a costume to not show skin. I'd just let her pick whatever she LIKES and would WANT to do and then brainstorm "how can we make this work" ?
Disclaimer : This post written by a Grumpy Old Man
Actually in the pipes:
- Remaking Ser Loras doublet.
- Luke Skywalker, A New Hope
- Wind Waker starter costume in swim material
Eventually: Paul from Dune, Faramir, Harry Sullivan