Oh my gosh, oh I'm sooo sorry!!!! I dont read every post every day, I'm sooo sorry
I understand she was 12 weeks? Its possible she wasn't fully weaned, or sometimes a young one will revert back to needing hand feeding when they move to a new home. Thats just one possibility... in tge picture it looked like maybe her keel was very sharp like she may not have been eat enough...and you talked about screaming in yiur other thread thst may have been her begging for food ( hand feeding formula food) young bird can play with food and it serms like tgey are eating when they are not or not eating enough... and sick birds can do the same thing, making you think they are eating when not really
or young birds can die at thus age from a virus they got or an infection that she could have come to you having.. these young parrots at Weaning age its a time they can die because their bodies are under a lot of stress from Weaning and their immunity isn't fully developed yet... i think the fall was a symptom that she was already pretty far gone not the cause of her death...the cold feet was her body already shutting down... i don't think she could have been saved even if you got her to tge vet right then...
I'm so very sorry for your loss.... so very sorry
O would clean the cage very very well every single bar and the food and water dishes and all the perches, and throw out anything soft thst can't be cleaned, just to be safe to your remaning bird. And I would take the remaining burd to an avain vet specialist to be safe incase it was Infectious.
If you ever get a second bird, it must be quarantined fir 30 days separate room from your first bird. Also get a digital kitchen scale, weigh your current burd every day for the next couple if weeks, and turn set up a weekly weight check. This is a tool to help pick up problems with your bird, because they do hide illnesses, until its to late...
A young just weaned burd should have weight checks every few days just be extra safe. This is advice for all the readers of your post...
Such an awful thing for you to go through
There us no way to know exactly what happened unless you had a post mortem done, but even then it can be difficult to get an answer,