My fiance has lower pelvic pain, faking to avoid sex? Any help?

What? Are you asking if she faking? Assume she is legit until proven otherwise. She needs an appointment with her ob/gyn.
Seek specialist. Pelvic pain is a real and common problem. My best advise is to seek help from a gynecologist specializing in the treatment of pelvic pain. You may have to consult a university hospital to find such a highly specialized physician.