At 2 years old, I would have expected her to have moulted last autumn.... late summer / autumn/ winter are the normal seasons for moulting but of course there are always birds that are exceptions. Can you post a photo of her? When you say she fell over, did she appear drunk/uncoordinated or...
It sounds to me like she is sick.
If she has lost a lot of weight and is skinny, the first thing to do is to giver her a heat source as she will be struggling to maintain her body temperature. Then hydrate and offer moist food like a mash made with her regular feed soaked in warm water or some...