Has your sister ever had gyn exam before? Does she have insurance? What is keeping her from the doctor?
If it's the actual exam, maybe you can get her on here and on a few other sites. There's a lot out there about what to expect from your first pelvic exam. Maybe something really simple is wrong with her and a fifteen minute visit to the doc could improve her quality of life. It could even save her life.
If your sister doesn't have insurance and can't pay, try to find her a clinic. I would make the appointment for her. My mom does it for our family all the time. Make it and tell her it is scheduled and talk to her about it. If it's a new doctor for her, ask the doctor if they have any booklets they can offer her to help her prepare.
I think it would be fun to make it special, too. Special toe nail polish or a sticker on her inner thigh, somethng to break the ice with the doctor. I got an e-mail once about a woman who mistakenly wore glitter to her appointment and it made the doctor laugh. I don't know if it was true or if glitter would interfere - I doubt it would since she wouldn't put it inside.
One more thing, many times the PCP can do the pelvic. I know mine does. If she has a doctor she is comfortable with, ask if they would see her for her current problem.
Just a few thoughts.
Total abdominal hysterectomy at age 26 due to abnormal bleeding. Kept ovaries.