Curious to what,
you are feeding them as a diet?
how often she gets in water roughly?
what antibiotic you have/are using at what dose?
The wing feathers happen to be affected first for some reason in regards to issues with the integument. There is a decent amount of fraying occurring; microscopically this is the barbs/barbules on the feathers separating each other. This can occur when there is a lack of oil distribution over them.
Lack of bathing, clogged oil gland, dirty environment, ectoparasites, and nutritional deficiency could all play some role in this.
In the picture the feather appears to have snapped, this could be associated with a nutritional deficiency of sorts created by a poor diet. Reason for my first question.
Deficiencies of minerals, such as calcium, zinc, selenium, manganese and magnesium, may be associated with brittle, frayed feathers and itchy skin. There may be alterations in color or discoloration of feathers. The plumage can appear dull. Feather loss and moulting disorders can occur.
https://www.beautyofbirds.com/feath...als, such as,and moulting disorders can occur.
If she was getting in water daily, I find it unlikely she would be experiencing such poor feather quality, which is why I'm curious how often she regularly gets in the water. If she is not getting in daily, I would ensure she does. Keeping a mister near the pen and misting her down occasionally (when warm) may stimulate preening activity.
As
@HollowOfWisps mentioned, improvement will likely not be seen until the next molt.