My best friend is 16. Her dad lives in California but sent her (forcefully) to live with her grandmother here in Idaho. Her mother , who does not have custody, also lives here in Idaho. Is it possible for her to move in with her mother or even me and my family even if her father in California says no. After all she is 16. Her grandparents think she is a sexoholic, alcoholic, drug addict. It isn't true and she is being treated unfairly. He grandparents even went as far as saying that no good man would ever want someone like her. She really need/wants to get out of there but doesn't want to go back to her dad who sent her here in the first place. Please help us.

At 16 she should be able to go to family court and tell them the problems that she has with her family and present a well thought out alternative plan so they don't think she is just going to end up with another set of problems. In some states if you can prove that you can take care of yourself under different circumstances other than your guardian they will let you get emancipated. I think you are suppose to have your parents permission for that but if they deem the circumstances bad enough they might do something about it.
From the little you have said it doesn't sound bad enough, but if it is family court is where she needs to start.