Roost being too high was a thought of mine regarding the trauma, but that wouldn't explain the feather loss.
I agree with the epsom salt baths and Vetericyn!
I would consider possibly treating with permethrin spray for parasites that may be there. Though I don't usually recommend it unless you confirm.. in order to prevent them from building resistance. But since it is safe, easy to use, affordable, effective against MANY parasites (except scaly leg mite, not your issue.. and depluming mites), and no withdrawal time for eggs.. I might consider this a special circumstance and treat without further evidence.
Alternatively... if you could afford to take even one girl to an avian vet... they might be able to tell you something. Cost at mine is $48. Though I can't take all my animals to the vet... sometimes when there is something widespread that you aren't sure of, they *may* be able to help. Sometimes it's a waste of time and $... hard to tell.