Thank you for writing. The problem is not the child’s attitude. This little girl is acting in a way that is perfectly normal when we look at the situation from her point of view. Her life is complicated. Since her parents are divorced, she has to go back and forth between two homes — whether it is convenient for her or not. Few adults would agree to such an arrangement and yet we expect it of kids. On top of that, you have vastly different expectations of her than her mother. Your way may be healthier for her, but from her point of view life is harder at your house than at her mother’s. I think she essentially likes you because you say she can be sweet at times. But it’s just true that the adults in her life have made things hard for her and, understandably, she resents it.
Ideally, you and your partner would sit down with her mother and create at least a few consistent rules around such things as bathing and tooth brushing, some basic chores and bedtime. When the adults can be adults and put the needs of the children first, the kids generally do much better. If that’s not possible, I think you should back off a bit and let your partner take the lead in teaching her and holding her to some standards. He is her father. You can’t be her mother. She has one. What you can be is a wise and loving adult friend. Instead of doing things for her (like decorating her room) in the hopes of winning her over, get involved with her on some projects. Find ways to give her a little more say in her life. As things settle down, you can take on a more mothering role, but for now it is only driving a wedge between you. It’s a little soon to be worrying about what she’ll be like as a teen. You and her parents have some work to do now.
I wish you well.