Do you think making her wear a black crystal necklace would hinder her abilities?

If not, then it's not magic she uses. Even if it's something that otherwise quacks like magic and walks like magic.
Hmm.. honestly i give it a 50/50 chance. We dont know enough about what black crystal do. Except its seemingly moderatly rare. Negate spirit on touch.
And are super toxic.

At the same time. No. I dont accept the definition of magic as "everything shut down by black crystal".
Not when we know so little about it.