I'm sorry that she isn't doing well.
From what others have said on this forum, dropsy is a symptom of a disease, not a disease in itself. So there are multiple causes of it.
If the medicine is the correct one to treat the underlying infection or disease, then yes, it can be effective. However, I've also seen others say that by the time dropsy occurs, the internal organs are affected by the underlying disease.
Have you tried using Epsom salt? It can relieve bloating and fluid retention. So even if it can't treat the problem, it may help make her more comfortable. (Epsom salt also has mild antimicrobial activity, and does not affect the internal organs that way that Aquarium salt does.)
If you want to try Epsom salt, here is one way to do it. This is based on advice that Oldfishlady has recommended to people whose fish had symptoms of dropsy:
- Add 3 teaspoons of Epsom salt to 1 gal of conditioned water. Mix/stir until the salt is COMPLETELY dissolved. Make sure the water is the same temp as her current tank water.
- Do a series of 25% water changes, using the treated water. Every 15-20 min, change out 25% of the current tank water, and replace with the newly treated water.
- Starting tomorrow, make 50% water changes every other day. (Or more often if she's in a small tank.)
- Keep her in the treated water for 10-14 days.
Also, put some plastic wrap over the top of the tank. This will provide humidity, and make it easier for her to breathe. There should be at LEAST an inch of air between the water and plastic wrap. (I try to leave several inches when I do this.)