My sister and her husband have 4 children together, and have been divorced for a year now. They have joint custody of the kids but her husband has physical custody of all of them ages 14, 12, 11, and 7. Three boys, one girl, her 12 year old daughter has decided that she no longer wishes to live with her father and wants to be with her mom full time. I believe she is of age to be able to choose which parent she wants to live with so how does my sister go about getting physical custody of her daughter?

There is no such thing as actually "choosing" until they are 18 and can do what they want at 12 the court may listen to her wishes but will also listen to the reasons they should stay with the father and why the mother thinks it is in best interest of the child.

So the mother has to get an attorney and file to motify the custody order changing physcial custody to her.