Moulting out-of-season can be a stress reaction. Has she been contained because of avian flu whereas she'd normally free range? Is she being bullied or has she been frightened by a fox, dog or child? That sort of thing. I suggest you keep her in a very sheltered spot, with maybe straw bales or similar around the coop and old feed sacks filled with straw on top of the roof to keep in heat but not impede ventilation. A good thick layer of clean shavings, a small handful of mixed corn before she goes to roost for the night and plenty of fresh water should help her get through it quickly. Some folks swear by Poultry Spice but I've never used it.