In my eyes, and I haven't had experience with viral- if you even get the chance to fully ID it as a viral... Sometimes if you get conditions just perfect you can get the viral to either die down a lot, or subside, and they can live a "normal" life- if it comes up viral though, and isn't responding to anything, I'd say euthanize it. Too many people put animals through a ton of pain/suffering for the person's hope, when frankly the animal would probably rather be put out of it's misery...
If she's been sick 4 months and nothing is working, I'd put her down myself..