Oakland nurse Maria Mendoza-Sanchez didn’t know what to expect, but as she approached Highland Hospital at midday Monday, she saw a growing crowd of familiar and unfamiliar faces who had come out to rally against her impending deportation.

Fellow nurses at the hospital were there, along with doctors, union members with “Hands off Maria” signs and protesters who’d heard about her case. The head of the public health authority that operates the hospital showed up as well, telling the crowd that Mendoza-Sanchez was being stripped of her “opportunity to achieve the American dream.”

Barring a last-minute reprieve, Mendoza-Sanchez and her husband, who do not have legal status, will fly to their native Mexico on Tuesday with their 12-year-old son, who is a U.S. citizen by birth, to start a new life after more than two decades in the U.S. They will leave behind three older daughters, all of whom have legal status.

The crowd at Highland, which quickly numbered in the hundreds, came to speak out against the action by U.S. Immigration and Customs Enforcement, which under President Trump has increasingly sought to deport immigrants — including those with deep ties to the country and no criminal records, like Mendoza-Sanchez and her husband, truck driver Eusebio Sanchez.

A spokeswoman for ICE defended the deportation order last week, saying the family’s case had gone through a lengthy review in immigration courts and that “neither of these individuals has a legal basis to remain in the U.S.” On Monday afternoon, the agency said the order remained in force.

After pulling up to the demonstration, Mendoza-Sanchez walked slowly to a table set up by union workers. “I’m Maria,” she told them, introducing herself before breaking into tears and hugging one of the workers. “I’m really happy to see you guys here. I’m feeling really hopeful.”

Delvecchio Finley, chief executive of Alameda Health System, which operates Highland Hospital, told the crowd that Mendoza-Sanchez had been a “stellar employee” in her two years at the facility.

“We are an organization of caregivers,” Finley said. “So witnessing this situation befall a member of our community has been extremely difficult for many of her co-workers, managers and executives. And for me personally. AHS values diversity and depends upon people of various backgrounds, many of them, like Maria, immigrants or children of immigrants, to provide care in one of the most ethnically diverse areas of the country.

“We want a system,” he said, “that affords hardworking immigrants the opportunity to achieve the American dream.”

After immigration officials said in May that the couple had three months to arrange their travel to Mexico, they decided that the best option was to take their son, Jesus, and leave behind their three daughters, who are 16, 21 and 23. The two younger daughters are U.S. citizens, while the older daughter, Vianney, is protected by the government’s Deferred Action for Childhood Arrivals program.

Daughters Melin, 21, and Elizabeth, 16, stood near a group of television cameras outside the hospital, watching their mother speak. Tears welled in their eyes.

“I just feel like right now it feels too real — like they have to leave tomorrow and I’m just shaking,” Melin said as her sister grabbed her arm. “They don’t want this to happen, and I don’t want this to happen. I’m not mentally ready to see them leave.”

The family made a last-ditch effort Friday, requesting a stay of their deportation, but as of Monday morning, they had not heard back. Their attorney, Carl Shusterman, said the case symbolized Trump’s shift in immigration priorities — namely, that nearly all immigrants without documentation are now eligible for deportation.

“As a former (Immigration and Naturalization Service) prosecutor, I am deeply saddened to see a family with three U.S. citizen children and no criminal record being targeted for deportation,” Shusterman said.

Sen. Dianne Feinstein, who met with the family last week after reading a front-page Chronicle story on the case, has called for the government to reverse its decision. The California Democrat said she would introduce a private bill in September to help the family gain permanent residence. However, such bills are rarely signed into law, and it’s unclear if that would help Mendoza-Sanchez and her husband.

“This is a mistake,” Feinstein said outside the family’s home on Thursday. “This shouldn’t happen.”

Mendoza-Sanchez’s nursing colleague and close friend Sara Norton, 25, drove her to the hospital on Monday, wiping away tears as they approached the gathering.

“She’s worked so hard to be where she is at now,” said Norton. “It is our job to be there for her — through all of this. We are losing our best nurse, and I’m losing a close friend for who knows how long. It’s something that’s hard to swallow.”

Beyond the rally, the family’s last day brought a multitude of tasks they never imagined — not only packing and cleaning but transferring parental custody of Elizabeth to Vianney. Meanwhile, Jesus spent his day with two of his Oakland schoolmates, playing video games.

Hamed Aleaziz is a San Francisco Chronicle staff writer. Email: haleaziz@sfchronicle.com Twitter: @haleaziz