Daughter wants to move in with her mom

Probably not a lot you can do if she wants to move in with your ex. Doesn't sound like it would take long before she realizes she made a mistake and wants to come home.Might think about taking your ex to court and getting custody. My ex threatened me the same way, then one day i said fine I'll get the ball rolling. that shut her up real quick. Just got to remember its all about whats best for the child.