this is a very large dog that has spent a great deal of time outside and was probably never taught proper house or social manners.
My best suggestion as a starting point, is to enroll in some obedience classes, as it seems you have a few issues to address at once.
Attending classes will help establish you as the leader, help define your relationship, teach you hands-on techniques to train, and how to deal with multiple problems.
btw, I think it's great you took this girl in!
