Hazel Black  - New Moon
Hazel's family and friends are her entire life. She'll protect them from anyone or anything because she hates to see them hurt. That's what fuels her anger toward Bella Swan, the daughter of her father's best friend and the girl who holds her brothers attention.
Hazel can see that Bella will never feel what Jake feels for her and it makes her angry to see Bella string her brother along the way she is.
Luckily for Jacob, Hazel meets someone who takes her focus away from him and Bella. He doesn't like the boy she's spending time with, but he's willing to put up with it since it keeps her from pestering him about his decisions. Until he finds out what Hazel's new boyfriend is hiding, then he's furious and reluctant to let them be together.
A boy Jacob doesn't approve of for his sister. A girl Hazel doesn't approve of for her brother. This can't be good for the siblings who were once best friends as well as family.