Will the father agree? He is unstable following the death of his wife and I think that no matter how much he knows it would be the right thing for his daughter to not live under his care, he's not just going to agree to it because he doesn't want to lose her too. My friend has tried to discuss this with her father but it's always turned into a big fight where he projects his own behaviors and actions onto her. For example he will tell her she's never around when actually he is the one who is frequently gone and not caring for the younger sister. It seems like he doesn't have any valid concerns or issues with her taking guardianship beyond having to give up control.