Can you post a pic....are her scales sticking up, is it her stomach or her whole body that is getting bigger....any other symptoms like-buoyancy issues, lethargic, hiding, clamp fins, not eating or pooping...etc......
What size tank, water temp, filter, live plants, additives used, how much and how often are the water changes, any tank mates, how long have you had her, is she in view or in the same water as a male Betta, what kind of food....
You don't want to soak the food- it can leach out the nutrients and vitamin/minerals. Pellets don't swell up inside the stomach like some may think-fish have lots of enzymes and gastric acid in the gut that break the food down for digestion-
If the food is high in grains/gran byproducts they can create gases that can cause the fish abdomen to appear enlarged and why you want to feed fish food with the first 1-2 ingredients to be fish, seafood base.....