Unfortunately, when you see pineconing scales, there is nothing much to be done except try to minimize discomfort. Dropsy is not a disease, it's a symptom - fluid buildup due to organ failure. Aquarium salt doesn't help at all, why would it? If anything, you should try Epsom salt, which reduces bloating...and while it certainly won't cure your betta, it might make her a bit more comfortable.
Maracyn 2 says it helps with dropsy, but honestly, fish almost never come back from dropsy. Kanamycin is another one that has a very rare chance of success. If I see pinecone scales on my fish, I euthanize them with clove oil, personally:
http://wetwebmedia.com/euthanasia.htm
You say your betta had fin rot before. For future reference, evaluate the setup - is this your betta in a 2.5 or 3 gallon tank? These are very small tanks, and while it's possible to keep bettas healthy in tanks that small, your chances of success are greatly increased with a larger tank. It may be convenient to have small tanks due to space and money considerations, but overall, bettas are best off in tanks of at least 5 gallons, with 10 and above being best, in my opinion. They live longer, and act more naturally when they have space to swim and plenty of water to dilute their wastes (which consist of things like hormones and metabolic wastes, beyond just the nitrates and stuff which we can actually measure).
