She is brought food by her mate and uses this opportunity to shed all their feathers and grow a complete new set. Penguins also moult in a disorganised way. They cannot afford to lose many feathers at one time because of the cold. They stand around in large groups with new feathers growing all over their bodies. These new feathers push out the old ones which the bird then removes by preening.
Most birds moult by replacing a few feathers at a time.
Moulting is normally symmetrical. Thus a bird may lose primaries and one or two separate secondaries on each wing - when these are replaced they will lose the next ones along. This way a bird can still function. The feathers grow quickly and it requires a lot of energy to build them, even so moulting can take a long time and some parrots take up to 9 months to complete a moult. Some larger birds of prey are an exception to the moulting every year rule and only moult their flight feathers every 2 years.