How much protein does she get now?
A breakdown of the nutrient content of the feed you give would be helpful.
There are lots of posts recommending extra protein feed to encourage feather growth. I have yet to find any evidence that this extra protein makes feathers grow any faster, or stronger than a properly balanced feed at sufficient protein levels for the breed.
Lack of sufficient nutrients in feed can be seen in semi feral flocks and in poorly fed flocks.
The indication of a lack of the correct nutrients is shown by feather bars/stress bars.
Here is a not particularly comprehensive explanation.
https://www.windycityparrot.com/blog/2012/08/23/feather-stress-bars-bird/
There is some anecdotal evidence that moulting birds go off their normal commercially produced feed and prefer other sources of nutrition found free range foraging.
I see this with the heavy moulting hens here. This may suggest that the hen 'feels' she needs something in addition to the commercial feed which while adequate under normal conditions is lacking in something under moulting conditions.
My solution to problem feathering is to supply in addition to a commercial feed, meat and fish which supplies a complete protein (all the necessarily amino acids) plus additional amino acids, minerals and vitamins. I would try feeding a few grams of lean cooked pork and/or oily fish such as sardines or mackerel.