A.M.
Does everyone live in the same house? If not how often/long is SD with you?
Does she have other siblings at moms?
Remember this is not just super easy for her either. What do you mean by "don't play well"? Does she hit, bite, push, shove? or is that she'd rather play alone?
All of these things can play a huge role in the reason why. First you have to find out the reason and then you can find a solution.