If you really have joint legal custody than conceivably she could live 50/50 with either parent? If I am right about that then she would already be living with you if she wanted and if her dad thought the environment was good. Based on what I am reading it still sounds like her father is the custodial parent and he is responsible for her welfare. The courts are notorious for siding with mother's in custody cases so the fact that she is not with you speaks volumes. And even if a child says they want to live with a parent the courts give only small weight to the wishes of a child in cases where the parenting situation is full of strife. So if everything was perfect and you, her dad and her all worked together then MAYBE the child's wishes would be given more weight. But with any sort of strife, neglect and stuff like that going on the courts will want stability over what the child wants because a child, even a teenager can be unfairly influenced by a parent, even a bad one.
I do not know the specifics of your situation but based on the small amount that I do know....if her dad didnt speak to you and say that you should offer her a place to live then it was extremely selfish of you to offer that. And confusing to the child.