I have a feeling that the divorce is pretty recent and there is still much animosity between the two ex spouses. I am not certain what age your child is, but regardless of age, if it was given to the child then it is the child's property and the child can do with as they want. However, the Ex is just putting the child in the middle of a dispute that is between herself and you and has nothing to do with the child (or the game). This is about control and power and has nothing to do with a game. The Ex is being selfish and is only causing harm to the child and in the long run is only damaging the relationship between you and the child as well as the relationship between herself and the child. I am not an attorney and have no legal experience, but I have been through a divorce with children and I can spot a power struggle and divorce tension from a million miles away! This is just my opinion and what I see from my perspective. Life is too short to fight about your child enjoying their game at which parents house!