Damn man, what is her reasoning for her hatred of you? Simply that you expect her to act her age?
He married her mom. I had the same problem with my stepkid.
We got married when she was 5 years old. She had her mom to herself for about 4 years after her dad walked out.
My mother in law didn't help either. She was insanely jealous of me and spent a good part of our early marriage trash talking about me to just about anyone who would listen. That included the step daughter.
She blames me for her dad not wanting to spend time with her. She blames all her emotional issues because the W/G traveled for, like, 4 years.
It's all bullshit and I'm done with it.