Should this child get her way?

I know a 12 year old naive child (lets call her Amy)with a learning delay and behavioral issues. Amy;'s father moved in with his girlfriend and her 3 kids due to health problems. Amy has acted out by not listening, gets suspended from school,makes allegations that are not true to people of authority about the girlfriend, when the girlfriend disciplines Amy strikes the girlfriend back.She is very niave.She is going through puberty and when the girlfriend sat Amy down with her daughter to talk about it ,the girl begged her dad to not let her period come and to take it away when it does.The father feels like he needs his own apt back due to the problems and drama she created. Is this the answer?I feel like she is acting out so she can have him back to herself.She is an only child.