Seven? Wow! I didnt think they lived that long! Average is 4ish?
Anyways, dropsy is usually terminal, even if you do think you cure it, usually it ends up popping back up within 6 months. Is she pine-coning? and how long has she been? If you catch it early enough theres a chance that you can cure her, but it sounds like she's had it for a while.
If this was me, which its not, I would euthanize just because of how hard it is to treat, i'm sure she's probably suffering now, plus she is 7, so even if you did treat you really have no idea how much longer you'd have left with her anyways.