I have a few questions that might help clarify some things.
Are the white spots you see ONLY on the leading edge of the pectoral fins? Or are there more scattered here and there across the body, fins, wherever?
I haven't seen any results for water quality and parameters. Whats the results for ammonia/nitrIte/nitrAte?
How about pH? And from the tap?
Do you know your KH?
How long ago was the pearlscale added?
Okay, off the top, since your fish is still eating, and assuming water is not an issue, you will need to start feeding her either some medicated food, or some homemade medicated food. Prefferably medi-gold. If you cannot get medi-gold, try searching locally for ANY antibiotics you can get. In fact, do you have any leftover antibiotics in any medicine chests anywhere? If so, what are their names?
Increase aeration if possible. Heat as well. Try 78-82F. But only heat after you have reached a 0.3% level salinity in your tank. Basically, all you can do right now is feed medicated food, perform extra waterchanges (temp matched), maintain salinity and heat and observe closely. If you are located in the US or a country that has antibiotics for fish readily available, try searching out furan two, or maracyn 1 and/or 2. Either of these would be a good place to start for a waterborne treatment. But pay close attention to the ammonia, nitrItes and nitrAtes when using these meds, perform waterchanges as needed.
Wether or not the white spots are ich, I suspect that the new fish brought a parasite or bacteria (or both) that your 9 year old goldfish has no immunity to. the key is to eliminate the problem as fast as possible so that healing can begin.
You might have to begin thinking about the age of this fish. At 9 years, this is an oldie. If it was subjected to questionable circumstances when it was young, it could be beginning to deteriorate from old age. But, the recently added fish is still making me think otherwise......
Post back soon.
Paul