I have legal guardianship of my niece who is 17, we are having continual behavioral problems and she now wants to move in with her dad that lives with my sister can she do this with out getting the court involved and with out me getting in trouble. Her dad lives in the same city she will continue to go to the same school

Who gave you guardianship? If it was your dad then he can recind it and your no longer liable. If he won't take it back then your still liable for her actions.

If you can't get the guardianship rescinded, then tell her to wait until she turns 18.