Mary Aversano’s doctors told her two years ago that she had about a year left to live. Her cancer is metastatic, spread from the uterus to the liver and lungs. Still, at 76, the San Rafael woman is mobile enough to get out of the house a few times a week — “It’s a rotten disease,” she said, “but I’m not going to let it get me” — and she did her own grocery shopping until recently, when the new coronavirus began to spread.

She worried she would catch the virus in a store, exposing herself and possibly her husband, who suffers from chronic heart disease. Her fears increased as the news worsened, and she considered herself luckier than friends who were more housebound or lived by themselves: “There are people out there alone and scared and disabled.”

Then, a few days ago, Aversano noticed a post on Nextdoor, the social network, where homebound residents have found a place to support each other and connect with neighbors.

A college student in nearby Fairfax named Alex Dewey was volunteering to pick up groceries, at no extra cost, for any neighbors at high risk for COVID-19, the respiratory disease caused by the new coronavirus. Aversano was reluctant to accept, not wanting to seem needy, but she got over that sensation. “You know what, you old broad,” she told herself, “suck it up and let somebody help,” and she asked Dewey to deliver a couple of food staples.

She wasn’t the only one. About a dozen elderly or immune-compromised men and women in Marin County responded to Dewey’s offer on Nextdoor, and more than 30 young people chimed in to say they could help if Dewey needed backup.

“Right now it’s stuff that I can do easily,” said Dewey, 21, who studies business administration and economics at the College of Marin, which is closed along with many other universities, its classes moving online. “There’s a lot of people who want to help.”

All over the Bay Area, “mutual aid” projects are sprouting up to help vulnerable residents get through the pandemic era, picking up the slack for slammed government agencies and overwhelmed corporations.

Dewey says she posted her grocery-delivery offer after thinking about her own grandparents, who live in the hard-hit Seattle area, an epicenter of COVID-19 cases. She has always been close with them, and her grandmother is an ex-smoker with lung problems.

“They’re from the generation where they don’t like to lean on anyone,” Dewey said.

A Chronicle reporter saw her Nextdoor post and asked to tag along when she went shopping for neighbors who had contacted her on the site. On Monday, the same day six Bay Area counties announced a shelter-in-place order that would take effect at midnight, Dewey left the house in Fairfax that she shares with two college roommates and set out to buy groceries and prescription drugs for four older women. Her mother, Cristine Platt Dewey, joined the trip to lend a hand. The family dog, Sally, rode in the back of their silver Prius.

The effort did not start out smoothly.

The first grocery store they visited, Good Earth in Fairfax, which had recently placed a large hand-sanitizing station at the entrance, was mostly picked clean, its shelves emptied by a wave of panic-buying. Same with the next store Dewey tried, Trader Joe’s in San Rafael.

She arrived at a third option, Andy’s Local Market by the San Rafael harbor, at 6 p.m., and saw to her relief that the shelves were full. She and her mother grabbed carts and started picking up items.

Alex, slim and brown-haired, wore a plaid shirt, jeans, white canvas shoes and black ski gloves to keep any virus particles off her hands. She had tried to find medical gloves, but they were all sold out.

“Mom said, ‘Oh, we could wash these,’” she said.

Other customers at Andy’s seemed anxious. A man with curly white hair and a black leather jacket said into his cell phone, “They’re out of roast chickens.” Next to Dewey, an older woman in an Adidas tracksuit pointed at the checkout lanes in the front of the store and muttered that not all of the workers were wearing gloves.

Dewey remained focused, plucking boxes and produce from shelves.

“People are tense,” she told the reporter.

Only half of the groceries on people’s lists were available. Broccoli was in stock; beans were sold out. At checkout, Dewey paid with a debit card, explaining that she was normally broke but could afford to pay for the groceries up front because she had recently received a $1,000 tax refund.

Dewey and her mother placed the groceries in four clear plastic bins in the trunk of the Prius, slathered their hands and gloves with sanitizer, and headed to a nearby Walgreens to pick up a prescription for customer Barbara Christopher. The shelves there were picked clean of toilet paper, and a large man waited in the checkout line wearing a full gas mask with double filters. Then they drove about a mile-and-a-half to make their first delivery, at Christopher’s home in San Rafael.

Dewey left a bag of groceries (butter, milk, orange juice) and the prescription on the front step. Christopher, 62, waited inside but didn’t want to open the door, fearing transmission in either direction. She had been healing from an injury for the past year. Instead she knocked on the window, threw out her arms in thanks and blew Dewey several kisses.

The next two deliveries were in the small, outdoorsy town of Fairfax, one at a single-story home near the city center and the second on a steep, wooded street, where an energetic and friendly brown dog bounded out the front door when Dewey arrived.

“Mochi!” called the owner, Sandy Handsher.

Handsher, 76, is a lung cancer survivor with part of one lung removed, leaving her short of breath and especially vulnerable to COVID-19. She said the last time she tried to buy groceries was a week-and-a-half ago. “I was trying to keep 6 feet between me and the next person in line,” she said, “and people just kept saying, ‘Are you in line?’ So I just put the stuff back and left.” Dewey delivered $45 worth of kale, cherry tomatoes, bananas, raspberries and sparkling water. Handsher thanked her profusely.

The night’s fourth and last delivery was to Aversano. By the time Dewey arrived at Aversano’s house on a quiet street in San Rafael, it was 8 p.m. and dark out. The porch light was on, and Aversano emerged, wearing dark glasses and a pink pullover.

“Oh my god,” she said, and thanked Dewey for the bag of brown sugar, maple syrup and her favorite type of yogurt.

“I’m a yogurt slut,” Aversano explained later. “As long as it’s honey Greek yogurt, I’m happy.”

Standing on the sidewalk outside Aversano’s house, Dewey said she felt the night was basically successful. She had spent $159 all told — three women reimbursed her by check, one by cash — and the shopping and deliveries had taken four hours, longer than she expected. Still, “It’s clear that there’s this need for it,” she said. “And more people are doing it.” She said she hoped to scale up the effort, organizing friends and other volunteers to make grocery deliveries near their own homes.

Older residents are doing their own organizing, too. Aversano is part of a Nextdoor group called Good Fairy, created by a San Anselmo woman to keep homebound seniors connected.

“It’s brand-new,” Aversano said. “We’re trying to get it all around the whole Bay Area. So people know there’s neighbors out there willing to do anything for them.”

She added: “I didn’t let cancer steal my spirit, and something with a stupid name like COVID-19” — she almost spat the word — “isn’t going to do it. So we need to keep people’s spirits up. That isolation feeling? That’s a biggie. You look out in the world and you think you’re all alone. No, you’re not.”

Dewey, she said, “was like an angel at my door.”

Jason Fagone is a San Francisco Chronicle staff writer. Email: jason.fagone@sfchronicle.com