You're not taking into account one very big difference here than most though, that is the money involved. Her father is getting rich off her, all her money he controls and he gets paid huge bucks over this charade. He's the driving force behind the involvement, and he is benefiting hugely from it, and is the reason why I think he needs to be removed from his role immediately and given to a neutral third party.
Is Brittany mentally unstable? I believe at one time yes, but I also believe that her circumstances and surroundings with the money and fame were environmental, and not naturally occurring. Do you think she would have been like she is if she never got picked up by a talent agent? I don't, her circumstances have changed now, her father should be removed immediately and she should be allowed to pursue legal proceedings against him.