She/he may just be bloated. How often and what are you feeding?
generally for dropsy there other symptoms like clamped fins, color loss, lethargy. The most common is called pineconning - their scales raise off their body and they look like a pinecone when looking at them from the top down. Are you sure its dropsy?
I would think it may be bloating/constipation. Try fasting for a day or two and see if the bulge goes away. You can also put the fish in epsom salt -
not aquarium salt (for bloating).
1 teaspoon per gallon. Mix the salt in a milk jug with conditioned water. once it disolves you can add the fish to it. be sure its plain epsom - not scented. Unlike aquarium salt, epsom can be used for weeks if needed.
Its said that their stomachs are as small as their eye. Insane!! So you may watch her diet. Only feed her what she can eat in a 2 minute period. Also, its known to be healthy to skip one day a week of feeding. its good on the digestive tract.
Yup. Sometimes they get swim bladder disease which is caused by over feeding and then they swim sideways, upside down, butt up, ect. Its usually not fatal but it makes the fish look pathetic.
are you using conditioner? its cheaper and usually better to use tap water with a good water conditioner the spring or distilled.
a pic would help if you can get one
One last thing - be careful with the bettafix. Petstores push it on customers but alot of people have reported betta deaths from using it, and alot of people claim its a miracle drug. It has a tree oil that can harm their breathing organ, so do not OD on it - follow the directions or maybe use a little less then the directions say. I wouldn't use it unless you are certain its dropsy and not bloating.