Tough one! While she definitely does need to hear it from someone, the best person is probably not you as she may take it personally and you risk losing your friendship.
I am not suggesting you call the authorities on her but may be you could arrange for someone who she is not friends with to visit her place with you. Even if they were not chicken people, you could give them the general gist of the issue and when you are all there talking about chickens, the third party could enquiringly ask questions about worming and mites etc, during which you could back them up; so not technically lecturing her, just feeding her information which she may digest.
Or, you could frequently mention stories you have seen on BYC about someone losing their chickens to worms or illness etc.
Educate and guide her in such a way that she does not even know she is taking on knowledge and hopefully changing her ways.
Baby steps