hard to diagnose on the internet because we can only go by what you know or notice. Try and see if you can get a clear picture of her to post on the forum, but until then, answering these questions may help
1. how long have you had her?
2. what size container is she in?
3. how often do you change the water?
4. how often, and how much do you feed her, including treats?
5. is there anything in her tank for her to hide in/among?
6. Is she breathing heavily, and/or is the inside of her gills red?
7. any white flecks that look like grains of salt?
8. any fuzzy or cottony looking patches?
9. does her belly look abnormally swollen?
10. if you look at her from above, can you see scales sticking out like a pinecone?
11. is she refusing food?
12. is she having any difficulty swimming (ie: upside down, sideways, etc.)?
13. is she flicking against anything in the tank (walls, gravel, plants, etc.)?
14. does she have any other tank mates?
15. do any of her fins seem to be shredded, red (unless she is naturally red), or disintegrating?
16. have you seen her poop, and if so, what color was it?
it may be nothing to worry about, there are many reasons for bettas to act the way you are describing. Some are very hard to deal with and others are nothing at all