About the mites, if the scales are raised on the legs put petroleum jelly on the legs. If the one or more of the chickens have body mites, dust ALL of them (with poultry dust/spray) and clean your coop and run out. Scrub the roosts and add poultry dust them and in the corners of your coop add a...
Welcome to BYC.
I read through your post and a picture is going to help the most. Your hen may have bumble foot.
http://www.the-chicken-chick.com/2011/07/bumblefoot-causes-treatment-warning.html
and she also sounds broody, staying on the nest all the time, she'd like to hatch chicks, you...