I am friends with someone who is nice to me but my friend group doesn't like them?

I am in high school and my friend group has recently kicked out a member(I’ll refer to them as z) because they think z is too problematic for them. The problem that is z has recently gotten closer with me and is kind and calm with me and I would feel way too bad and guilty to leave her for the others, she also doesn’t have friends outside of our group, but I fear if I stay with z my group might hate me. I don’t want to lose either of them, but I don’t know how to resolve this. What should I do?