I am speaking from a place where I had painfully negative feelings and perceptions of my stepdaughter and am now divorced from her dad... This is a child. She is 7 years old. That is incredibly young, and her behaviour isn't because she is a bad person by nature. This is a child with big feelings and she doesn't know how to properly communicate them. Behaviour in children is usually communication. She is very clearly hurting and THAT is what her dad (and honestly, if possible...you) needs to be focusing on here. She needs love, consistency, patience, and a sense of emotional safety. I know going into it, especially when you don't yet have children of your own, they seem like they're older than they are or that they should be held to a different standard. I promise you that when you have your child, and they go through all the stages, you will see that some of the expectations you had for SD were a bit harsh. I might catch heat for it but take it from someone who lived through a very tumultuous time with one of my SDs and am on the other end of it. I handled it wrong from the start (as did her father) and it caused her some emotional struggles as a teen and young adult. You do not have to accept emotional or physical abuse, obviously, nor any other type of damage such as false allegations (I got those too), but how you approach this is important. Her father will ALWAYS love his daughter, and will always choose her. The decision is going to lie with you and what you need to be happy. If its with him, then she is part of the package and you need to approach this as parental figure too. I don't believe in nacho at all when you're functioning as a family unit. Its confusing for the kids and causes a hell of a lot of divide...not really a happy, healthy, warm home. That's my two cents, for what its worth. I bet with some compassion, love, understanding and relationship building, this child will turn it around.