that definitely works! cammie's father is the ceo of a real estate development company that has been in his family for generations so it's definitely feasible that lissie's mom could have been shunned. the other option is that cammie's mom came from a lower class background but she worked her ass off in college, married rich, got into politics and is now a senator. and once she got married, she pretty much disowned the rest of her family and broke off contact with her parents and siblings (one of which could have been lissie's mom). so it's totally up to you which direction you prefer.