not liking step child

I have a son from a previous relationship that's 5. I have been with my partner for 3 years. I've been a step mom to his daughter for 2 years. (shes 4) It's been a really tumultuous experience. the biological mother withheld and manipulated the child which us why there's a year that I wasn't in his daughters life. for those past 2 years we have regularly had her on weekends. I have a 4 month old baby with my partner. so anyway, I have tried really hard to bond with her. I spend more time with her than my partner because he works so much. I provide for her in every way that a parent should, I do fun things with her, I try to interact in as many positive ways. I have also tried giving her space and letting her initiate the relationship which also didn't work. it doesn't help that she has behavioral issues because her biological mother doesn't discipline her. she gives her anything anything she wants and when we've asked her why she says That she had nothinhgg growing up so she wants her daughter to have everything. It's gotten harder and harder and I have considered leaving my partner over it because I don't think it's fair for her to grow up with a step mom she doesn't like and I don't know what else to do. does anyone have advice or even just know what I'm going through....................................just want to point outthat I mentioned I've been iher step parent for TWO YEARS. I am married to her father. I've had a child who didn't act like that. I parenting time is for step parents too. she has a step dad who has her most of the time. If we based parenting time on when my husband isn't working we would never have her.