Sorry, I cannot say for sure either what caused her death and therefor if what you did had any negative effect on her - my guess is probably not - as others have said, they do go into a death spasm sometimes and it seems like your hen was on the way there when you tried to help and you may have actually slowed it down by a short time, I doubt that you caused her death - it was probably on the way and you were just there for her at the end - maybe the warm bath at least felt good to her at the end
I never heard of a bath or calcium killing a bird like this - maybe a whole bottle of tums, but not a small amount - it is good to have doubts and to ask for input from others to learn and possibly help more effectively if it ever happens again, but other than that, I think we need to take a deep breath and accept that we cannot always change what life has in store and that is not our fault
I can relate to the doubts about the amounts of meds and help given, but please don't panic - you did the best you could in a very difficult situation with limited information to go by and with the threat of losing a loved one if doing too little and if doing the wrong thing and if doing nothing, so something had to be done and that is all any of us can do
Agree that necropsy would be your best bet to find out more - sometimes state vets do it for free - call your state agency and find out - it needs to be done soon after death and/or the body should be keep at refrigeration temperatures - and to be honest, they don't always solve the mystery, but often they can
don't be hard on yourself please - I have been there and many others, I am sure, as well - when a bird gets sick, by the time we see it, it is often very sick and sometimes too late because they hide it so well from their flock mates (part of nature to stay alive) - then when we try to help, we are really in a tough spot - good for you for trying to help! I wish it had ended differently, but you did what you could and now the other bird still needs you - my husband keeps telling me, when I am upset about a loss, to focus on the ones that are still there
still, I understand, and it is ok, I think, to miss the ones we knew that are gone now - they are all such characters and special to us