When can a child decide who they want to live with?

I have a neice, who is 14 years old (will be 15 in Sept), and she hates going with her dad. Her dad has already said that he doesn’t like her, has called her fat, and told her she would get pregnant by the time she was 14 (now he’s changed it to 16).

Her dad is now remarried to a woman to doesn’t care about this girl. The dad has taken mom to court and gotten custody of the oldest boy (2nd oldest child out of 6 total children), because he said the mom was not capable of caring for him properly. However, supposably the other kids are just fine. If Hunter, the child he has custody of, doesn’t want to visit his mom, he’s not forced to. However, if Melissa, the oldest girl who’s 14, doesn’t want to go with her dad, he threatens to call the police to force her with him.

At what age can Melissa go to the courts and request that she lives with her mom? They live in Arizona, just for reference.

Any advice would be greatly appreciated and sorry it’s so long.

P.S. She is so against spending time with her dad, she ran away from his house this morning and walked 8-10 miles away. It wouldn’t have been that far, but she would walk to a gas station, and nowhere would allow her to use a phone until she reached Chevron.