my step daughter's real mom see's her every second weekend and bad mouths us (her biological father and me, his fiance) to our child. She plays victim in terms of not having money to fetch her daughter or buy clothes etc and our 10 year old is therefore constantly trying to side with her mom after listening to her manipulative explanations of how her lack of effort is our fault. We don't bad her mom to her and just correct or explain when we do things the way we do and refrain from speaking on her mothers behalf, we don't bad mouth her mom either.I can see this pains her and her mom wont think about her actions and how it affects her child. what can i do as a step parent?
Can your partner speak to his ex? Explain that this is all making DD very confused and upset? Ask what support she wants/expects from you?
I do think it's important for DD to see both her parents but I really understand the manipulation that some parents use to make their child side with them. Your partner should be sitting down with his DD and asking her how she feels about everything and then gently putting her right with correct versions. For example if she says that her mum can't see her more because you won't let her then he explains that if she wants to see her more then they can work something out but DD needs to see her dad on weekends too. If it's about money then explain that mum has to support herself and also contribute to bringing up dd and you are doing what you can.
Without having any more information it's hard to know what to advise. But kids like to know what's going on. They don't like being stuck in the middle of parents. If she won't open up then suggest school offers her some support or counselling where she may feel more open to discussing whats going on in her head.