Update:
So I got the phone call this time so I have some more detailed (ish- its early, forgive me.) information.
First, the most important part- she is up and walking, holding her head up pretty much all the time now, with the exception of her 'snuggle my biiig scary beak and ruffle my head feathers for me' time, that absolutely nobody has the heart reject the request for. So that is great news! She would be going home tonight, however they were able to weasel another night out of the pet store.
While I miss her, I also would rather her stay as long as she can in professional care while she gains strength and some weight.
The labwork they have been checking was just basic bloodcounts, sugar levels and white cell numbers that were critically necessary when she came in. The store just now authorized (finally) more in depth blood work. It appears they were attempting to save some money but are starting to really see that their business as a whole is in danger (though again, overall I place my blame with the breeder as their other birds are older and healthy).
They started antibiotic injections last night as she is still regurgitating some though they haven't been able to test positive for infection yet. As infection status is still unknown and a possible other cause for the regurgitation is also likely (small crop, body relearning how to digest food) the antibiotics are largely preventative as it will take her immune system time to recover.
While I don't typically approve of such use of antibiotics I feel in this case it is appropriate as they are so late getting approval for the needed tests and infection is reasonably likely. She had one dose last night, and will have two more today and the course will be ended with one or two tomorrow depending on what time she goes home (assuming the pet store stops the money fountain after tonight). If tests come back showing no infection, then she is to just have one dose each day to keep it that way, as last night's dose could have largely cleared up any weak infection and stopping too soon after would allow it to come back likely stronger.
I did not get numbers on how her weight was doing, I was more worried about the above information and it slipped my mind. Vet's goals today are to continue feedings and watching sugar levels, though sugar has been stable and they are weaning her off the added sugar in the formula slowly. They are going to begin doing some more standard tests (I don't recall the names- I'm sorry) to get an overall picture of her health and to check for any defects as no one has faith in the breeder she came from.
While 'we did everything right' it was likely the stress of coming home and such a great change that triggered this. Stress caused her to burn more energy then at the pet store and thus, she spiraled so suddenly and so quickly. If she had remained in the pet store it likely would have happened over night but a bit slower, rather than Monday afternoon they likely would have come in Tuesday or Wednesday morning to find her gone in the night.
According to the vet, the extra feedings while in our care are likely the reason they were able to bring her back at all, let alone so quickly. Again, for that, I owe you all, who were kind enough to tell me I wasn't out of my mind in feeling like one wasn't enough. When we pick her up, I'll see if we can get a copy of her records and the bill so we can see what all exactly she was tested for, those results and for giggles, the cost of this adventure.
Vet is still going after the breeder. She has a name but is choosing not to disclose it to me, wanting us to focus on our baby and leave the vet to her. She has contacted the authorities and I have released Koko's records for them to use in going after the breeder. Sadly, best case is that they find birds in poor health, in horrible conditions, the breeder gets fined and their birds taken away. If they find the birds in somewhat decent conditions and not obviously in horrible health the breeder may not receive anything but a scare.
Koko is 16 weeks old tomorrow. She has been in our care for about 12 hours under a week. She was in the pet store's care for a week and a half total prior. Our neighbor had her for half a week. In total, she has been away from the breeder for 3 weeks. According to the vet, she would venture to say that Koko has been critically underfed for 4-5 weeks. In her opinion, this appears to be the case of a breeder attempting to force wean a chick starting at 10 weeks of age, if not a bit earlier.
We'll probably have another update tonight around 5.