Winston sees and hears a large (Winston at first calls her "monstrous"), older prole who hangs laundry and sings in the courtyard below the window of the room above Mr. Charrington's shop. She seems to be constantly hanging diapers. She has a good voice and makes the popular tune she sings sound "almost pleasant."
This woman is important because she provides such a sharp contrast to the average Party member. She sings spontaneously, something that Winston notes Party members never do. Further, she seems happy and at peace with her life, a state of being also not usual for a Party member. As Winston puts it:
One had the feeling that she would have been perfectly content, if the June evening had been endless and the supply of clothes inexhaustible, to remain there for a thousand years, pegging out diapers and singing rubbish.
Right before he is arrested, Winston shows he has become fully re-humanized when he realizes the washerwoman, though a prole, is fully a human being, and he even thinks of her as beautiful. He realizes that she lives the kind of ordinary, everyday life surrounded by family which was once the normal way people lived, and he realizes that it is her kind that holds the keys to future. He thinks to himself as he watches her:
If there was hope, it lay in the proles!