She still tithes to her church, even as other members have cut back. She rarely worries about rising gas and food prices. And she never bothers to balance her checkbook, because she doesn't come close to spending what she has.
"I live so far below my means that it doesn't really register," said Ms. Rainsberger, a 31-year-old Chicagoan with a wiry frame and unusually sunny outlook. "I don't have to think about money."
How is this possible?
For starters, she has no car and commutes by bicycle each workday. She also has no mortgage payment and chooses to live in an "intentional community," a partly shared space where $775 a month covers utilities and meals.
"In one fell swoop, I pay for the roof over my head, the food in my stomach and the lights to read by. That's a big advantage," said Ms. Rainsberger.
Her high-rise living space is part of the residential program at the Keystone Ecological Urban Center in Chicago's Uptown neighborhood. Her private quarters -- larger and a bit more expensive than some -- are about 400 square feet, divided into a sitting room, a craft room and a small bedroom. She shares bathrooms, showers, a kitchen and a large dining room with 28 other residents whose ranks include young professionals, professors and retirees.
"It's like a college dormitory, but with better conversation," she said.
Of course, the concept of sharing resources has been around since the beginning of time and is used today from Amish farms to the Israeli kibbutz. For low-income families, it's often simply a matter of survival.
Those who track consumer habits say a growing need to cut costs, along with a wish to be more environmentally and spiritually conscious, is causing even more people to pool their resources, whether defined as an intentional community or not.
"The economy starts to tank. People get tired of it," said Daniel Howard, an expert in consumer research and behavior at the Cox School of Business at Southern Methodist University. "It's people saying, 'Let's get together and help one another.' And it works."
Few may have the desire or even the ability to live the Spartan lifestyle that Ms. Rainsberger learned from her Depression-era grandmother. Not everyone is willing to bicycle, for instance, in the stifling mugginess of a Chicago summer or the cold, blustery winds that sweep off Lake Michigan in winter.
Those who advocate a simpler, less consumer-driven life say there are lessons in the strategies she and other intentional communities use.
By buying their food in bulk, for instance, Ms. Rainsberger and her neighbors spend $100 to $150 per person each month for meals. (Consider that the U.S. Department of Agriculture "thrifty plan" for a single person is $200 a month.)
Some residents who own cars also share them, drastically cutting overall vehicle expenses.
While this particular intentional community has no children, similar communities trade childcare or keep costs low enough so more parents can stay home or work part-time.
The Fellowship for Intentional Community, a Missouri-based nonprofit that began a steadily growing directory of such communities in 1990, estimates that at least 100,000 Americans now live in one.
They define them as groups of people living together who share common values that are religious, economic, environmental, social or any combination of those. Sometimes they own property; others rent. About a third live in urban areas, while the remainder are rural.
Laird Schaub, the Fellowship's executive secretary, says he has no proof that the growth in numbers they've seen is tied to the economy. But he has little doubt that intentional communities are better equipped to weather hard times.
"We're pretty isolated from the ups and downs of the regular economy," said Mr. Schaub, who has lived at the Sandhill Farm intentional community in Rutledge, Mo., for 34 years. The farms' 10 residents grow most of their own food and sell organic produce to the surrounding community. Some have other jobs and all share their income with the group, as do about 13 percent of the intentional communities in the Fellowship's directory.
"You don't have to chase as many dollars to have a quality of life," Mr. Schaub said.
That is freeing in other ways, says Duane Elgin, an environmental activist in California who focuses on simplicity.
"It isn't just cutting back on things. It's about people not needing so many things and putting more attention into their personal interests and their family and friends, being creative, being of service," said Mr. Elgin, the author of the book Voluntary Simplicity, a concept he began fostering 30 years ago. "As a result, they are richer individuals."
Lela Philbrook, a 23-year-old singer who lives in Ms. Rainsberger's intentional community, has found that to be true. She saves so much money living there that she's able to pay for voice lessons, which cost more each month than her room and board.
"That's huge," Ms. Philbrook says. She lives down the hall from her grandmother, a longtime member of the community whose room is a frequent gathering place because she has an air conditioner and wireless Internet access.
Residents also regularly congregate to play games, do puzzles and watch old episodes of Alias or Veronica Mars.
Ms. Rainsberger, whose closest family is in Ohio, savors the camaraderie.
"For me, to be able to walk out my door and have everybody in the hall know me, that's a really great experience," she said. "And if anything happens to me, I know there's somebody next door who'll take care of me."
Certainly, there are times she's had her fill of community and the inevitable difficulties that arise with any group.
"Then," she says, laughing, "you go to your room, shut the door and don't come out."