Partner and I have been dating for 9 months. He moved in with my DS, 7 and myself quite quickly and AFAIC, it's going okay.
I know my partner has some issues surrounding feelings of insecurity, but most of his issues were caused by her treating him so badly for years. He also finds dealing with some situations difficult, (authority figures telling him what to do) but he's really trying to make good changes and we are working on these problems together.
One of the situations he has struggled to deal with is that of his ex girlfriend.
Partner and ex girlfriend have a 2yr old DD and tbh she is crazy!! A real loon.
She made it difficult for him to see DD, but since I met him, XGF took him back to court 
and agreed to let him see DD at weekends.
XGF has since behaved very oddly and I'm not sure where we go from here.
A selection of her behaviour is: Attempting to tell me he is a thief/liar/cheat. Partner has told me XGF has begged him to go back to her, so I can only assume she is trying to put me off, but it hasn't worked, I'm prepared to stick by him. 
She has told me my DS probably hates him (DS adores him) and that he will only get me into lots of debt (I pay my own way, unlike herself.)
She complains Partner doesn't pay maintenance (He has not found a job that has suited him for long enough to pay) then she said he stole money from her. (Where will it end?)
Partner and I noticed DD had a few bruises on her body, her inside lip was cut, and she had a cut on her head, so we reported XGF to Social Services. They have carried out a full investigation. Partner doesn't trust them though (you hear the stories in the news of them getting it wrong) so Partner also made a report to the doctor about DD development.
Now nutty XGF wont disclose who DD's optician is, even though Partner has every right to know.
We have resorted to refusing to respond to any form of communication, unless it is through a solicitor, because of the abuse she gives us on picking up DD. (we do not have a solicitor at present due to financial constraints) and XGF solicitor has costed and closed the case.
Her abuse is mainly to tell me to keep out of it. I am just trying to support my Partner. She has led him a rough ride, and I am more than happy to help him.
I do not class myself as getting involved, I am just supporting my Partner as best as I can. (He would like full custody and I believe he is a good dad to DD) I have also written a few letters to XGF (from Partner of course, but he is terrible at letter writing), have answered his mobile when he does not want to speak to her, and we chose to put her hair in French Plaits, which Nutty XGF says is too much too young. 
DD looked beautiful.
I don't think XGF is a good mother. She shouts and swears in front of DD, doesn't appear to care about her very much, and smokes. (I have seen all of this with my own eyes btw).
It has got to the point now where XGF will not speak, and we do not speak to her, but it is a strain. Obviously, there are day to day things we need to know, especially when DD comes to ours, and although we have asked XGF to respect our request not to make direct verbal contact, or telephone either of us, she simply refuses to do anything. I have written to XGF, and she is being churlish and childish to refuse to reply. (Another example of how she doesn't care for DD much at all.)
How do we proceed from here? We can't afford a solicitor, but she is taking our written word to the ludicrous extreme.
What do we do to make her understand that we will not tolerate her abusiveness and total lies about Partner, and to see it is for the best for the forseeable future for Partner to see as much of DD as she does. (Partner very hurt about this.)
We have proposed to her in writing that DD lives with us for a week, then her, and hopefully that will get the ball rolling, but again, she has not responded to our request.
How do I get through to someone so stubborn and unreasonable?
I want the best possible life for her DD, and I know that is with me and my Partner.
Maybe I am just ranting, I just wondered if anyone had any words of wisdom for me and my Partner??