I'll throw back to you that I don't want to sound rude...
You need to try to work your daughter through her issues with being examined, the sooner the better. I know that gynecological examinations can be embarassing for grown women, but I also know that a lot of "female problems" go undiagnosed & untreated for just that reason. You can look for a female doctor for her if she thinks that will help, and if your insurance allows for it, take her to an actual gynecologist instead of her family doctor for any problems that may crop up in the future. It's all business to the doctor, yk? Some of the most seemingly innocuous infections can lead to real problems if left untreated, and you want her comfortable to go to a doctor when necessary (she's already coming to you, which is great!).
OK, off my soapbox now.
If she isn't having any pain or redness to go along with the swelling, then it's probably just one of those things. Have her check for things like ingrown hairs & feel her labium carefully in case she's got a cyst or something. (Which I think is unlikely.)
Now, it is
perfectly normal even in grown women for one side to be fuller than the other, and this may well be a forerunner of that. But if she has any real worry, then it's better safe than sorry, and perhaps a chat with a gynecologist could help ease any other concerns she has.