another post with another question!

hi sorry for all the posts with the constant questions!!

one of my hens stated mouting in september - just on the bum/underneath area, and its not grown back? i considered all the other possibilities other than mouthing like lice/red mite/worms etc, and nothing she seems perfectly healthy eating drinking running around the garden, jumping etc but still bald underneath and she looks half the size she did a few months ago, is this still mouting? as im baffled no signs of ill health but why is she still bald and smaller in size?

they have all been wormed with flubenvent sorry for spelling! and i treat the coop for red mite but i dont have any anyway and i put the mite powder on the hens, ive checked all under her wings her vent everywhere and theres no lice or mites so i dont no whats wrong my other 2 are fine

What is her weight like compared to the other two chooks? She may just seem smaller if she has been losing feathers all over but not gone bald in all areas?