I know it will be zero consolation but… even when you are the biological parent, children (and most especially teen girls) can be a total nightmare. My own parents were utterly useless in ever regard so I made huge efforts to be a good parent for my own two children, especially post-divorce. With my son, things worked out very well and he’s an amazing young man. With my daughter (and there was no favoritism, no different treatment) the results were the precise opposite. For the last 4 years we’ve had no contact and she appears to be continuing (according to those who still do interact with her on occasion) as though she were a sulky 13-year-old despite being 22 now. In short, being a parent or step-parent is tough, often unrewarding, and your mileage will inevitably vary. Hang on in there!