A North Carolina cosmetics saleswoman in the Big Apple for a brief business trip was thrust into the crisis of a lifetime — and discovered the inner beauty of what she thought would be a city of cold-hearted strangers.

Shelcie Holbert, 23 years old and six months pregnant, arrived on June 17 with three days’ worth of black clothes — her unofficial uniform as a sales rep for the Kiehl’s cosmetics company.

She was excited to visit the company’s East Village flagship, but as soon as she arrived, she felt a strange pressure in her abdomen.

She excused herself and walked several blocks to the emergency room at Mount Sinai Beth Israel. Doctors put her in an ambulance to Mount Sinai West on 10th Avenue, which specializes in preterm labor.

Doctors found she was 3 centimeters dilated. Her due date was still 17 weeks away — Oct. 12.

“You do know if you have the baby right now, she is not considered viable,” a specialist told her.

Holbert’s husband, Jacob Wallace, an Army veteran who had served two tours in Afghanistan, flew to New York. She was able to hold onto the pregnancy another week, long enough to give her daughter a fighting chance.

Holbert delivered Rosalie Grace on June 26 at a mere 1 pound, 9 ounces, just a bit larger that her mom’s hand.

Rosalie was whisked down the hall to the neonatal intensive care unit, or NICU, where she would begin her battle to live. Her chance of survival was estimated at 50 percent to 70 percent.

Meanwhile, her parents had their own survival to think about in an unfamiliar, and costly, city where they would have to live for at least the next three months.

“I had no idea how expensive it is here,” Holbert said.

She said the hotel where the couple stayed for the first few days cost $4,000 a month.

But help soon arrived.

Kim Kaplan, a Hamilton Heights mom whose twins boys were born early in May, started chatting with Holbert in the NICU lounge and was floored by what she heard.

“It just seemed so overwhelming to me, to be in New York and not have anyone you know,” Kaplan recalled. “I just felt terrible for her.”

That night, she put out an appeal on the UWS Mommas Facebook group, a community where Upper West Side women trade tips and seek advice.

An army of New York moms rushed in.

Jenna, who lives near the hospital and owns a second apartment in her building that she is trying to sell, immediately offered it to Holbert and Wallace.

“My husband thought I was a little insane at first,” Jenna, who asked that her last name not be published, told The Post. “I can’t explain it. I knew it was the right thing to do.”

She and Holbert were soon talking several times a day like old friends, and Jenna was going to the NICU to visit baby Rosalie.

Upper West Side mom Toby Baldinger read the appeal and wanted to make sure the new parents had a hot meal every night without having to think about dinner. She gave her credit card to a nearby diner and told them to deliver the day’s special to the apartment every day for two weeks.

Homey dishes like pot roast and penne pasta awaited the couple after they returned from long days at the hospital.

Other moms started delivering home-cooked food, and one is even baking treats for the NICU nurses. Even more women donated gift cards and clothing suitable for a nursing mom.

Meanwhile, Rosalie is making steady progress and already weighs 2 pounds, thanks to tube feedings with her mom’s milk.

And a heavy dose of New York City love.

Dr. Rafaela Calabio, one of Rosalie’s doctors, thinks the support is helping Holbert relax, produce milk and care for her baby.

“It’s incredible what they’re doing,” Calabio said. “How comforting.”

Holbert said she was surprised and grateful for all the kindness.

“We live in the South. You have this idea that New Yorkers are abrasive and they’re scary,” she said. “The level of support I’ve gotten from complete strangers is absolutely crazy.”

Another challenge is on the horizon as Wallace returns to North Carolina this week to start a job and Holbert needs a new place to stay, as renters are committed to her temporary apartment in a few weeks. She is confident something will come through.

She won’t lose touch with her host, though — she has asked Jenna to be Rosalie’s godmother.

“New York City is not what I thought,” she said. “I’m glad my daughter was born here.”

Donations can be made to the family at a GoFundMe page for Baby Rosalie.