she is not good at having sex
Most Helpful Girl
Thats a really shit reason. Do you actually care about her? If you actually care, you can work with her on this. If you don't actually care, do her a favour and leave.
The fact that you even ask this makes me wonder if it's the latter.
Sex is a type of communication. If you give more detail on in what ways she's not great I might be able to help more clearly.1