i agree with suetheramble why make things difficult for her aunt even though you both do not talk to each other , i think you will find she is entitled to expect you to help with her upkeep until your daughter has left further education , if it was me i would sign over the child benefit to your sister , although reading on your daughters behavioural problems i think it unlikely your sister will put up with her for long!! Although it may go the other way and she turns into an angel for your sister , all depends on the boundaries she sets for her and whether your daughter accepts them from her as opposed to you!