She is probably doing it because she likes the work. She feels good earning a bit of money even if she doesn't really need it. The sense of fulfillment is probably worth a lot more than the actual monetary value. Lots of us derive happiness from work or from feeling useful.
I know at least one old timer (early eighties) that gets really happy when heading over to exchange his bag of aluminum cans. He lives in his daughters home and he doesn't really need money. My thinking is that it makes him happy to earn a bit of money completely on his own, at his age.
Indeed they live with family and the can money go to gambling at all those Chinese seniors clubs. A woman who used to clean out the cans here now hires other women to do it and runs a little recycling empire that ends up on the Mahjong table.
There's also a culture of no waste from that generation my friend's grandmother was more than wealthy but refused to eat with plates snacking with newspaper plates she made and grew a large crop of food in their front yard selling it to corner stores every year. She also would dig out clothing out of trash bins, wash and slice up the fabric to sew different clothes she also sold but didn't need to being fairly wealthy.
I know at least one old timer (early eighties) that gets really happy when heading over to exchange his bag of aluminum cans. He lives in his daughters home and he doesn't really need money. My thinking is that it makes him happy to earn a bit of money completely on his own, at his age.