Pictures of her, the preening gland, her legs/feet (tops and bottoms), her vent, etc.
The bathing may help to initial kill the mites, but it sounds like she keeps getting re-infested? You may want to try Ivermectin to see if that helps, but eliminating the mites/lice from the housing is going to be crucial in controlling re-infestation.
Use your Permethrin to treat the housing/nesting boxes and roosting bars. You 'll have to clean out all the bedding. Re-treat everything 2 more times in 10 days intervals, hopefully that will eliminate most of them. Do any of the other birds she's housed with have mites too? It would be a good idea to look.
Her age is not helping and neither is the weight, but at 6 years old and being a suspected Red Ranger she's lived quite a while

The slight smell of urine is a bit concerning, is her vent area staying soiled?
You mention that she likes to roost high, with her size and weight, how does she get up high - do you place her there or is she able to get their on her own? How does she get down - jump or you take her down?