Strange bald patches

One of my White Stars started with bald patches under her wings and it's now spread round her bum. There are no feathers in the coop/run so she isn't moulting.
UNLESS she's eating them. I watched her preening and she was concentrating on the bald areas and seemed to be pulling at feathers. There's no blood or anything.
None of the other birds touch her, she's laying well and perfectly healthy, recently wormed and Frontlined.
Could she be moulting and eating the feathers? Or is it something more sinister......

Mavis never really had feathers on her underside at all, area looked red, but never bothered her. Poppy when broody will have less feathers but they grow back.

Check for crawlies as that can cause feather pulling.  I hope it is just molting but best to check.