The maggots: It's called fly strike here is some wiki info https://en.m.wikipedia.org/wiki/Myiasis
Holding them upside down can harm them if it's too long but I don't think that's the case. Chances are due to the Fly strike she had she was anemic, discoloured comb would indicate that, I'm not...
Honest I don't see how chickens would be any different than any other animal that spends a lot of time around humans. I realize a lot of people don't think chickens are very smart however I think every animal who spends a lot of time with people would be capable of trying to communicate with us...