It looks like she is being plucked by another chicken. Watch to see what is happening, especially during roosting time. It could be due to not enough roosting space, boredom and sometimes feather eating.
Provide them with some extra protein to give them a boost.
Photo#4 looks like she has Scaly Leg Mite - there are many treatment options to get rid of those. General care is to wash the legs in warm soapy water, gently scrub the legs with a soft brush the loosen the debris under the scales (mite poop), then apply some type of oil (A+D ointment, coconut oil, vaseline, castor oil, cooking spray, etc.) to smother the mites. The oil would need to be applied daily for a couple of weeks.
Treat the coop with a Permethrin based poultry spray or dust. Check the hens for any lice/mites that may be on them as well - if you find any, treat with Permethrin as well. (Permethrin treatment will not kill the leg mites that are on the chicken).
When I ask about the abdomen - you would need to pick her up and feel her bottom toward the back end - see if it's distended, bloated, swollen or feels like it has fluid in it. You may have to compare her to another hen - LOL Any chance at all that she is laying eggs in a hidden nest somewhere?
http://www.the-chicken-chick.com/2013/03/scaly-leg-mites-in-chickens.html
http://www.the-chicken-chick.com/2012/08/poultry-lice-and-mites-identification.html