Ok, this sucks. That breeder should be banned from breeding...They didn't even want the pain meds for the bird, just the bird? This might be the worst breeder story I've ever heard, and I'm sorry you're dealing with this, as well as your poor bird.
Was this an certified or qualified avian vet that you took her to, or was it a general vet or an "exotics" vet that sees birds? I'm asking because it doesn't at all sound like an experienced avian vet if they did no physical exam and did no culture to test for respiratory or gastrointestinal infections with a downward tail.....That being said, I wasn't aware that your bird was having pain and swelling in her tail area. Is she? Obviously you would see swelling, but does she show pain when you touch her tail area? Does she have ANY OTHER symptoms at all besides the pain and swelling in her tail area, like liquid coming from her nose or mouth/beak, sneezing, coughing, wheezing, labored breathing, being fluffed up, being lethargic and not playing, not eating normally, sitting on the bottom of the cage, etc.?
The reason I'm asking is because if this vet did no physical exam, your bird actually has pain and swelling in her tail area, but has no other symptoms as of now, it's very possible she has an infected or impacted Uropygial Gland. This will definitely cause pain and swelling in that area but will only be caught if a proper physical exam is done in the early stages. This is also called the "Preen Gland", and it's located on the bird's lower back just above where her tail starts. It's a gland that excretes an oil that the bird rubs on it's feathers when it's preening itself. While she is preening herself, you'll normally see your bird reach her head around and poke this gland a bit with her beak, and then continue on preening her feathers. She's getting some of the oil on her beak and then she's rubbing the oil on her feathers while she preens. It's a waterproofing mechanism.
It's easy for you (since your vet didn't bother) to check her Preen Gland out. I'm pretty sure your bird is hand tamed so you should be able to hold her in one hand and look at her Preen Gland with the other. If she is not tame or she will not let you hold her in your hand you'll have to get a towel and burrito her inside of it with her face exposed, like a Babushka, lol. Then turn her over and pull the towel up, exposing her tail and lower back.
Looking at her back, go above where her back ends and tail starts and move her feathers away until you see the gland. Sometimes there's a white feather or tuft of down sticking out of it, sometimes not. If you see a single white feather or tuft underneath her regular feathers just move the white feather and look at the gland underneath it. If you see no white feather then just move the feather away, looking at the bare skin on her back, until you see a little bump with a pinhole in the middle of it. You can't miss it, it's just sitting there on her back.
Normally the Preen Gland protrudes a bit but should not appear to be swollen, have any redness, have any type of boil, cyst, or lump on or in it, and should not have anything in the pinhole, like a chunk of white or yellow stuff. If it looks at all like an infected pimple or a pimple ready to pop, or is very swollen or red or has a plug of stuff in the hole, then it's probably infected or impacted. Also, press on the gland gently with your finger and see if your bird shows any pain response. It should not be sore at all. You can actually gently squeeze or "milk" the gland and a small amount of completely clear liquid or oil should come out. Usually if you just press your finger over the hole you'll get some clear liquid on your finger. This is normal, but if anything else comes out that is not clear, but rather white or yellow or looks like blood, is thick, or is like a rock or a plug of junk, then it's infected or impacted.
This is usually easily treatable with warm compresses and antibiotics, but the vet would never diagnose it without looking and doing a physical exam. But the pain and swelling at the base of the tail sounds probable.
Also, did your vet at least look at her vent to check for swelling, redness, any discharge, etc.?
"Dance like nobody's watching..."
