“She’s having a bath,” Sevier recalled the guard as saying, a luxury one official told her is available only to babies removed from their guardians. In the facility’s standard cages, there is no soap or showering for the kids. Though 72 hours is the longest a minor can be legally confined in such a facility, some had been there almost a month. Sevier waited.

Finally, the guard returned with news. He had found the girls after all. “We located the bodies,” he said, in paramilitary slang. “I’ll bring them right in.”

I visited Sevier’s medical practice last week in the border town of Brownsville, Texas, 60 miles from the Ursula facility, where she’d been a few days before. In mid-June, a team of immigration attorneys had asked Sevier to come with them to their next appointment in Ursula, after they’d had an alarming visit there earlier in the month. They wanted a doctor to evaluate the children and then use the findings to force the government to improve conditions in Texas immigration facilities. It wasn’t the kind of work Sevier usually does.

Sevier grew up in Brownsville, and to Rio Grande Valley kids like her, then as now, the border was not a crisis but a culture. Sevier went to nearby Matamoros, Mexico, for dinner, dentist appointments, weddings, and baptisms. Each year on All Saints’ Day, she scrubbed relatives’ tombstones in Matamoros with soap and water, then shot BB guns with her cousins at the cemetery. She had American classmates who lived in Mexico and commuted to school over the international bridge.

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She left the area for college and medical school. From afar, she told me, she began to understand that she had grown up in one of the poorest places in the United States, where low-quality, high-calorie food leaves kids both hungry and obese. Diabetes is widespread, and because access to health care is so limited, diabetic amputations are far more common than in the rest of the country. She thought that here was a place in need of a doctor like the one she was becoming. So after she completed her pediatric residency at the University of Texas Southwestern Medical Center, in Dallas, five years ago, she returned home.

The morning I visited, Sevier’s pediatric clinic was bustling. A mural with characters from the Disney movie Inside Out, about the emotional lives of children, brightened the hallway. For Sevier, the role of a pediatrician includes “being the voice for the kid, the advocate.” In some families, she explained, children’s experiences “are just not valued.” A child who is overweight or has a preteen crush may be the subject of ridicule, not attention and understanding. “I get to chip away at that in my office,” Sevier told me.

She tried to take this same approach in Ursula. Neighboring the immigration facility are cold-storage warehouses that keep produce fresh despite the oppressive Texas sun and triple-digit temperatures outside. Opened under former President Barack Obama, the Border Patrol warehouse is chilly too; migrants have long referred to it as the hielera, or ice box. Even its official name sounds agricultural: the Centralized Processing Center. But while the crisp produce moves swiftly across the border, a reminder of the close ties between Mexico and the United States that Sevier knows so well, the migrants inside Ursula spend their first nights in America stuck beneath lights that never turn off, shivering under sheets of Mylar.