Sounds like she's dropping them off of her brooding tracts, the breast areas hens use to brood eggs.
Doesn't mean she will go broody, just that hormonally her body 'thinks' it's soon to be time for brooding; however she may have other ideas. (She may not have the strongest instincts so may never go broody no matter how often her body prepares for it).
She may or may not go into full moult at the same time and drop all her feathers, hopefully not in one go but one by one.
Best wishes.