The best thing for her would be to make her get used to it, the best way is to make her wear it at night since then she won't have to worry about how she looks. I think she should first understand that the more she wears it the quicker she can get rid of it, that's the reason why I started wearing it much more often. If she's uncomfortable wearing it at school then make sure she wears it as much as she can at home. Banning her from her phone might make her see the twin blocks as a negative thing, she should view it as something for the betterment of her dental health. That's what I think.