I would leave for a few nights and tell them they need to figure it out. Seriously, I love that you want to be the answer but not sure you can be the answer. For reasons stated above if she is not your biological daughter I would be careful.

Little girls are the sweetest or the most stubborn creatures on earth. Finally at 11 mine does not fight quite everything that's asked of her. She for the most part refused to stay at her moms house for the past 10 yrs basically, now this yr she is excited to go and brother refuses to go so maybe they are just getting older and enjoy being around the same gender parent as they age.