We've all been there! @Miss Lydia has helped me out of a duck jam, or 2, or 3, or....... ;) Hopefully Charlie will continue to be fine - but keep us posted on what the vet says - we all learn from each other here!
:hugsIf I had just lost a bird to an illness, then had another showing similar symptoms, and I still had the medicine left, I would definitely give it to her - I don't think it would hurt.