But one question..if there are mites on her would all of my other chickens have mites as well? Should I check them all? I’m assuming yes?
Yes, it's always good to check them all.. once a month if possible.. My personal experience required no treatment for about 5 years and then one year lice showed up.. after 2 treatments with the permethrin based spray product (according to directions), several years went by before any treatment was needed again.. impacted by things which include wildlife pressure, soil type, weather patterns, etc.
According to studies I've read.. 90% of parasites were found on 10% of the flock in California back yards.. this is due to different genetics, different immune systems, different foraging and bathing habits.
If one is found with parasites, then it's advisable to treat the entire flock.. so that untreated birds don't become otherwise easy targets to keep the parasite lifecycle unbroken.
Anecdotally and for example, I recently had to treat my dogs for fleas.. One dogs was loaded (she has some lousy genetic issues causing poor quality dry fur), A second one with good quality fur had barely anything but still some activity, and the third had nothing (super shiny slick fur). The one that was loaded with the poor quality fur also spends lots of time under the shade tree while the other 2 do not. They all 3 sleep in the same bed and all got treated.. which unfortunately means a trip to the vet because nothing over the counter works in my current humid location, despite having excellent results at our previous desert location.
Another way to check for those night time (roost mites) is to wipe under the roost using a white paper towel and look for smears on the towel.
Though less common.. depluming mites will never be seen by the naked eye, according to my current understanding.
If it is a mini molt.. then you might be able to see some pin feathers starting to come in. I'm not personally sure how long between losing them and regrowth starts to become apparent or if it's immediate. In
my experience, molting does not cause "angry" skin.