hmmmmmm...odd.
This is a very good site (with pictures!)
http://www.fishjunkies.com/health.phpalso
http://bettatalk.com/betta_diseases.htmit doesnt sound like anything i've encountered. is it possible she scratched herself on a decoration? (maybe they arent related, just happened to occur at the same time?)
regardless, i would do frequent water changes, maybe every day or so. small ones, about 5 or 10% and add aquarium salt and extra stress coat or something similar. I have realized that bettas' immune systems are USUALLY pretty good, and often they can heal themselves given a clean, stress-free environment. im not saying dont treat them, just that sometimes they just need a little help instead of chemicals. GL! if you find out what it is, or can post a picture, that would help us a lot. i really wish i knew more to tell you. how big a tank is she in? are there any other fish in there? if so, do they show any signs? what are the water readings, like ammonia, nitrIte and nitrAte? ive had trouble getting on here, so im sorry for the delay. Keep us updated!
Amber