Do I let his sister live with us still and keep the phone we got her?

So my fiancé’s sister got out of a very abusive relationship and has been staying with us for 3 weeks. Well her phone was broke so we added her to our plan and she got an iPhone 8 Plus. Well she has gone back to her abusive wife for the millionth time (we’ve gone through her staying with us for a week then leaving again so many times I can’t keep track). And I’m upset and want her to move out and stay away from us because my 5 kids get so attached to her then she leaves and I’m sick of them getting hurt. So should I not let it bother me and let her keep the phone (that she hasn’t put a dime towards even though she said she’d pay us) or do I ask for the phone back and make her stay away?