I think your ex is being really irresponsible. He knows there is an issue between his girlfriend and his daughter and any man worth anything would be doing his UTMOST to protect his daughter. Going to watch the football and leaving his daughter with a girl who he knows dislikes her is just such lazy, lazy parenting.
I definitely don't think your dd needs to be anywhere near a meeting between you all; she has said to you what the issues are, the adults don't need her around to say it again. I think she would find any meeting really stressful....But well done to you for keeping your head screwed on and dealing with them so diplomatically. Others are right, the girlfriend is not emotionally mature enough to give anything to your dd because she wants to do all the taking.
Whatever happens, your ex needs to step up and take care of his own child for the limited time that he does have sole responsibility for her. Your child is very young, is coping manfully with living in a split family situation and would probably find it hard even if she had the BEST step mum in the world. She needs her dad to help her now.
Lucky girl that she's got a mum who is making sure things are done to help her..good luck.