Step daughter taking advantage of us?

My step daughter lives with us not because she likes us but because she has no other choice ... She is full time student, and works part time . She doesn't contribute with a penny in the house ( we pay all utilities , rent and even her phone bill ).she doesn't have anything to so with the house period(cleaning,laundry,wash dishes,even flushing her toilet etc...), she is very mean to her mother . Now it's the tax season and she is saying she is filing her taxes alone so we can't even get a break from her being full time student at least tht what I think. So what do u suggest us to do ?! And can we still claim her as dependent and get break from her being full time student ?! Any advice or suggestions ?! Thank you Note : last year was the only hear she handled us her college papers and said to us to claim her but this year she is going back to her old habits filing her taxes alone . She has been living with us for 6 yrs now and he father the one who lives overseas and comes here for few months a year claim her instead ...