My GF moved to her dad's in OK. but her grandma in California has custody papers. Can she take her back?

Alright so my girlfriend lived in Palm Desert CA, and we went to the same school. She lives with her grandma, but then her grandma went to jail for 60days for smuggling Mexicans over the border. (I know its sad). So my girlfriend was watched over by her aunt for about 40days and then her dad in Oklahoma took her, but has no legal custody over her. Her dad is very cruel and mean to her everyday and she's miserable there and wants to come back and she might be able to now that her grandma is now out of jail, but can her grandma take her back since shes has papers showing she has legal custody over her? Can the dad deny her grandma from taking her even though he doesn't have legal custody over her and the grandma does?? PLEASE HELP! THANK YOUUUU!