It seems to me that yourself and your former spouse are putting the needs of the children first... high five for the both of you... children suffer as well and you're both mitigating the trauma. As others have said... your girlfriend is playing a power game, and she obviously has insecurities which she refuses to communicate. I agree that her circle of friends is more than likely getting a colourized version of the situation, as is her therapist.
Re: therapist... if the therapist refuses to interview you, either in party or alone, perhaps the therapist is seeking to keep the girlfriend from straightening her hash out. my two shekels at any rate