Hello and welcome to FF! Dropsy is caused by a bacterial attack and when it's rarely caught on time, can be cured with antibiotics. Once the symptoms (water retention causes bloating) manifests themselves, the damage to internal organs taxed with osmotic regulation is permanent. In other words, even if you stop the bacterial infection, the animal will have permanent renal malfunction and will probably die from it.

Do not use salt when dealing with dropsy; that will make water retention worse. Some relief can be had by using Epsom Salts at the rate of 1 teaspoon per gallon. Distilled water is not good with frogs in the long run; even if it reduces the swelling temporarily. Treating tap water with Seachem Prime is a better choice.

Not sure if you are dealing with irreparable organ damage after first incident or, if some bacteria did survive the Maracyn 2 treatment. If they did; it's probably not a good choice anymore and another antibiotic is required if bacteria are present. Maybe you could try Melafix mixed per the label instructions for a week and see if there is any improvement. Melafix is a mild natural plant extract and has been proven useful against some bacteria.

Sorry your long term pet is not well; but if the frogs internal organs got damaged, there is no treatment that will reverse it. Good luck !