I'm dating this guy who has a daughter. She resents the hell out of me. I'm always nice to her but she disrespects me a lot, especially when he's not around. I've tried to be the adult but she's testing my limits. Absolutely this could interfere with our relationship. ?????
My guess is that you're talking about a pre-teen or a teen. She's being very protective of her mother and is also concerned about you "stealing" her father. Just be patient and kind. They usually come around. Some take longer than others.