Partner’s daughter

So I know I’m not trying hard enough to love my partner’s daughter. I so want to mainly for myself because I know it feels way better to love others when you love yourself which is what I want to work on. I tell myself this but then keep looking for evidence as to why I don’t like her or think that she is a bad parent when this is none of my business. I want to think she is amazing just as she is and that she’s doing her best raising her two young boys at the tender age of 26. Her boys are 8 and 5. I feel so much judgment towards her and her mother still which obviously feels terrible. I feel judgmental that she got pregnant in high school and never graduated, that she expects people to do what she wants whenever it suits her, that she can’t pack appropriate clothing when her kids come stay at our cabin or even toothbrushes. It’s like whenever she does something like that, I just think she’s awful. Whenever one of them acts up, I think she’s such a bad parent and always lets her kids get away with murder. I want to change my story about her so I can feel unconditional love towards her. I feel like whenever I’m in a not so great place with life, I “hate” on her more than usual. I even try to get my partner to scold the boys so they get proper parenting which, who am I to say how a child should be raised when I don’t have any of my own. I also think, she’s just like her mom, which I have been told she is. I have many people in my partner’s family tell me how spoiled my partner’s daughter is and that her mom was so awful to my partner which doesn’t help with me looking and finding evidence for how terrible they both are. It’s like I want to punish my partner’s daughter and her mom for something that I don’t even know what. I’m the one who feels like I won life’s partner lottery because my partner is amazing, kind and sweet and when his ex decided to cheat and leave, I in turn, get an amazing life partner out of it all. Oh I should add that sometimes I’m not so nice to my partner when it comes to his daughter and I want to stop the bad talk about her altogether because in the end, this girl is his daughter. Thanks in advanced for the advice.