Okay, so if she was yours and knowing everything I have done so far what would you do next? Im so stressed out about it
I would think E.coli would be treated with a antibiotic but im not sure. I haven't had a sick pea until her so this is all new to me.
If it were my bird, I would finish out this second round of antibiotic in this bird, I would treat EVERYONE for coccidia, and I would worm ALL the birds.
And I would look at every bird really, really closely for any signs of illness: sneezing, mucous, watery poo, listless, ruffly feathers, lack of appetite, icky feathers below the vent, eye drainage or irritation, weird breathing... anything that didn't look exactly right....
Doctors use different antibiotics on different diseases, because not every bug responds equally well to every antibiotic. It could be that the one she had is responding to the Tylan just a little more slowly than some other bugs might.
It's also possible that having coccidia or worms made her more susceptible to the respiratory infection.
She was originally with the other bird, and the other bird has been with your other birds. If it's coccidia, everyone has been exposed, but maybe some of them have more resistance, since birds develop a natural resistance to coccidia. But it won't hurt any of them to get treated for it with the Corid, and it may help them keep from getting sick.
I'm certainly not a vet, and there are lots of other folks on here with more experience, so maybe they will have other ideas?
I hope she continues to improve.... but you gotta do something about that poo before she gets sicker again.