The skin will stay bright red until she molts out all those chewed off feathers. Does she have complete bare spots where the feather is chewed all the way down to the skin? This is a classic sign of depluming mites. My birds butts and bodies stayed bright red and irritated until a good molt. After a molt, the skin returned back to a nice skin tone. It seemed to be the bareness of the skin that caused it to be red, not any mites. You will know you have the mites under control when she stops the incessant chewing and picking of her feathers. It is something you have to watch to see, and will happen over time and treatments.
I tried all the sprays and powders with no luck. Again, these mites rarely even get on the skin, so powders and sprays aren't powerful enough. Ivermectin soaks into the skin and blood stream and stays there a lot longer. I wasn't sure about the length of time for egg withdrawal, however since I was treating my birds once a week for a while, I didn't eat any of their eggs until 2 weeks past the last dosage.
After the following molt, I saw very little feather damage from these mites, there was a bit of it however. I still to this day treat the birds just to keep up with the mites. A couple times a year I will put drops behind the neck to keep the nasty bugs under control. I believe my mite issues comes from the wild birds we have around here. We are overflowing with wild birds.