I agree with the other postings that it could be ovarian cyst, possibly endrometrosis. My sister had pain on left side, but no fever and it was endrometrosis. She recently had surgery to remove the endrometriosis and feels much much better.
Okay, not to scare you but my other sister had severe pain in her left side and it was colon cancer. PLEASE if she is NOT having bowel movements, starts vomiting, bleeding rectally, etc then insist on a colonoscopy. I've had one and it's really not bad at all except for the prep isn't the most fun. My sister was only 38 when diagnosed and a friend of mine had a son at 9 years old with severe abdominal pain went to emergency room and doctor realized it it was colon cancer possibly and ran test. It was colon cancer! So it can happen at any age. Again I'm sorry if I'm scaring you but I'd rather you be safe than sorry since that type of cancer can be slow growing. I'm sure she doesn't have that, but if she shows any signs....please get her checked!
Now I also had a friend who's brother had to have appendix removed and it was on LEFT side instead of right like normal. They said sometimes it's like that in some people...strange, but you never know.
You and your daughter are in my thoughts and prayers. Keep on insisting she gets treated until both of you feel better. It's mother's intuition to know that something isn't right with her child. Good luck and I hope she feels better soon!