How old is your granddaughter? (I'm guessing a teen?) Is her father your son, or son-in-law? Do you feel she moved back to him because she wanted more "freedom" and you were too strict? Did her father know that was her motivation? It sounds like he may not be around as much to supervise, and she's taken advantage of it. Is she living close enough to keep in touch with her old friends, or has she found a new group of friends who are not the best influences? She may feel like she doesn't "fit in" with regular girls if she hasn't got her mom or another positive female role model in her life. If living with you again isn't an option, I strongly urge her dad to seek professional assistance, such as a family counselor, to try and re-establish positive communication and respect in their relationship...