Pre Teen Daughter with alot of bottled emotions?

[Jen B]

My oldest daughter, 11, has had a lot of changes in her short life. a Biological father that wasn't in her life until 2 yrs ago. A divorce from the Dad that adopted her. My job moves us every few years. Making friends is easy for her its leaving them thats hard. Her Biological Father is in and out but after my divorce Her adopted dad was not around as much so she longed to know more about the other. My ex remarried a year ago and didnt consider how it would affect the kids. My Oldest is bitter and feels she doesnt matter. Her grades have dropped drastically. Therapy was a waste because she shut down completely. My ex just gets frustrated and blows it off. Now she wont even answer when he calls and she throws a fit when she goes to his house. She will talk some to me but then my ex thinks Im causing her to be like this. What do I do? Shes only 11 but should I force her to talk to him or see him. I dont want her to think she has control but I also dont want to make it worse if she is already struggling with her feelings with her dad