What may be wrong with these feathers?

[jbird]

Our 2 year old Silver laced Wyandotte has never seemed to recover from her molt this past winter. Her feathers are stringy and weak. I have checked her and the coop, both at night and during the day, for mites and lice. I haven't found anything. We have two other chicken who don't seem to have the same issues. The areas that seem to be most affected are around the neck and under the vent area as well as her tail feathers. Sounds like lice or mites to me. I would think the others would be affected?! Any clues?

 

[Indiana hens]

1st guess would be parasites feeding. Worm her lately? Sray her with permethrins to get rid of mites or lice. Dog shampoo with permethrins also works for chickens. 2nd I would suggest high protein feed and maybe some yogurt for the best feather building. OOps, ***3rd could be egg carrying bacteria: ecoli, salmonella, etc***. Now that I think about it move #3 to #1.

 

[jbird]

What is the best organic treatment for egg carrying bacteria, ecoli, salmonella?