Thank you for getting back to me. Yes, the picture did attach, but I also looked at the one on Flickr. There's no way to be certain without having an aquatic vet examine and perhaps biopsy the growth, but it looks most like an actual tumor to me. If it were caused by gill parasites, Orca would be rubbling on things and probably having difficulty taking in enough oxygen.
If it's bacterial, the treatment you are now providing would help, but it doesn't look like anything bacterial I've seen, plus most bacterial infections cause other symptoms. Viral is a possibility. the most common virus in goldfish is carp pox. But carp pox growths are usually waxy and this doesn't look waxy in the photo. If it is viral, there is absolutely nothing you can do about it. However, your other fish would have already been exposed. Actually, most goldfish have been exposed to carp pox, but many ahve developed immunity. If that's what it is, most fish live healthy lives with it, unless the growths reach the point that they interfere with movement or breathing.
A tumor can be removed by an aquatic vet if it begins to bother Orca. This link will take you to a directory of fish vets if you decide to go that route:http://www.aquavetmed.info/index.cfm?PID=6
Many goldfish live for years with benign tumors. If it's cancerous, surgical removal wouldn't offer a permanent solution.
Only you can make the decision about what to do, but I'll give you my input. If this were my fish, I'd continue the full course of treatment with Melafix, Pimafix and salt. If the growth doesn't change during that time, and Orca develops no more symptoms, it's probably safe to put her back in the pond. Of course, there are no guarantees because nothing is ever certain with any living creature, but I'm inclined to think this is a tumor. If she is a very special fish to you, you may want to consult a vet.
If you have more questions, let me know by clicking on REPLY. I hope the growth will not cause any problems.