Mia: you probably know by now this hits right at home for me, too.
Your child is in therapy with a good attitude toward it at an early age.
YOU are her mother (the best thing she has going for her). I think you are doing what you can, by listening to her and getting her a professional to help her with her feelings. I think just by this, she will fare better than my daughter has (and she's ok, don't get me wrong).
My son (almost 17) does not want to cause any trouble. He will complain about dad to me, but wants to just keep it quiet around dad....he will stay "under the radar" to get out of his dad's way. That and play a killer jazz sax. He is "outta there" mentally (and almost physically) anyway. He did have some success with a therapist, and has developed some coping mechanisms that work for him. He just wants to be happy, and pretty much ignores everything else. As much as his dad makes him uncomfortable, he will not speak up to him at all.
My (almost 13) year old daughter, however, is much tougher. She was only 3-4 when he left, and doesn't have a dad in the house memory.
She is tougher for her dad to deal with and it has been clear all along, my ex has no idea what to do with a girl. She has tried to speak up to him, but any personal expression that threatens his fragile dad ego, has had serious repurcussions for her.
So my daughter has learned:
Do not speak up at all around dad and step mom unless it is to placate them.
Mom understands, tell her, but dad doesn't listen to mom either.
I will be punished for asking to go "home" when I am supposed to be at dad's. (long, traumatic story) I will never do that again.
(you can see, Mia, why I would want an evaluator involved...PAS or no PAS).
And she has also told me: "I have my way with dad. I know how to talk to him. I say what he wants to hear, and don't really listen to him." (sound familiar?)
And SHE WILL NOT SPEAK TO A THERAPIST!!!! Shuts down, won't talk, absolute refusal. She will talk to me, but since dad won't listen to me, really, it is still safe to do so, perhaps.
She has recently been studying with a professional theater group and doing extremely well. She is also in several choirs....so, she is not failing to find some voice, somewhere! This is her therapy for now, I guess.
I'm happy you have a therapist to help your kids, but always remember the addage: "kids really only need ONE VERY GOOD PARENT" (and that is you)....and then I add this part: " and they will be especially fine if that one very good parent is no longer married to a very bad parent!"