Find your local Avian Veterinarian
certification, species, credentialing, veterinary clinical practice, vet, abvp
Here are two listing to find vets but I would stick with the first one if at all possible.
People throw around the word 'rescue' too much and it seems that word has lost it's true meaning. It concerns me this lady got this bird just recently and has not gotten it proper medical care when she recognizes there is a problem. That is why she will not give/sell you the bird - there could be legal consequences if she does. She is just interested in brokering birds it sounds like to make herself money, that is why she wants you to take the Scarlet, to cut her loses if the B&G dies and any others she has have been infected.
Your heart is in the right place, to want to help a bird, but you must be aware that you could potentially spend thousands of dollars and a broken heart on an innocent bird that, because it did not receive medical treatment much sooner, will not make it.
R2rusmc - I don't see any pictures either. I doubt if a bird is 2-3 years old it would be staying of the bottom of a cage even if it had no perches, the bird would at least be climbing on the sides of the cage. Neurological problems? Toxicity? There could be hundreds of things and I for one am not a vet to even begin to guess what might be the problems here. This woman has no business having birds if she does not provide necessary care to a living creature whose life she has been entrusted.
The decision is yours how you want to procede, just be fully informed and aware of what you may be facing. Good luck.