It seems like you're allowing yourself to be used by this teenager. It's ridiculous. She's obviously turning everything on to stay out of trouble. Her mother turns on you. But you're allowing this teenager to blow smoke up your a&&. Why you continue to trust this teenager is beyond me. She's a kid in trouble. It's up to the mother to handle her not you. I, personally, would say moving out and away from them would be better for you.
Good Luck
Ocean