As it seems, despite all your extraordinary efforts and care she is declining.
I am very sorry.
Did the vet take a swap and fecal samples at all to determine the kind of bacteria she is dealing with?
I would continue for another eight days, as this is going on for a long time already, so the...
Yes, for the moment they are better.
You can use the other supplement on a regular basis like twice a week for your flock in winter
Yes, one can overdose, but not with a few days of supplementing the much needed calcium for proper egg shell formation.
To me this sounds as if she is laying internally or trying to lay eggs without shell.
Do your chickens gave grit and calcium like crushed oyster shellls available at all times?
Might be albumen/egg white.
At 4+ years in your care and unwell from the start you have done a good job keeping her...