Her hens are most likely stressed from having so many roosters. We had 13 hens and 2 roosters, they were so much healthier when we got rid of our roosters, sadly not all roosters are good ones.
Maybe you should take some roosters out of there. There is a lot of them, and they are to aggressive when mating. When rosters mate with the hens a lot, the feathers start to get scratched off of their back.
