The next day, Shays saw the girl back at the camp. His reaction, he said, was, “Why are you here? You went over there, and they said they would take care of you.”

Perry feared that with the girl’s infection worsening, another fistula could open up and drain excrement directly into her abdomen, triggering sepsis. Rushing her to a hospital in the U.S. was not an option, and doctors in Matamoros had told her they did not have specialists who could do the operation. “If she were to fistulize into her abdomen, we would not be able to save her life,” Perry said.

The two-page MPP guidelines give wide latitude to the judgment of CBP officials when it comes to granting exceptions. Those eligible to bypass the policy include people with “known physical/mental health issues,” and even “other aliens at the discretion of the Port Director.”

“What does that mean?” Perry wondered aloud. “Does that mean the 2-and-a-half-year-old boy who has uncontrolled seizures living in the camp? Should he get admitted? What about the pregnant women?” Perry told me CBP had not communicated any clear standards. As far as she could tell, exemptions were subject to the whim of the supervisor on duty.

I emailed Customs and Border Protection to ask which factors the agency considers when granting exceptions to MPP. How sick is sick enough? A CBP official responded that “all claims are handled on a case-by-case basis” and declined to discuss the girl.

The Matamoros encampment is volunteer-run—neither the American nor Mexican governments, nor the United Nations, is involved in providing food, housing, or sanitation. Brownsville residents cart over hot meals, and charity groups help out with water and toilets. The mobile medical clinic is an RV that Perry drove down from Florida with her dad. Humanitarian workers coordinate shifts through Facebook. On Monday, they decided to draft a petition on the 7-year-old girl’s behalf and post it online. The agency, Perry said, tries to “avoid bad press,” and advocates thought the media attention would change officials’ minds.

The following afternoon, as news outlets made inquiries about the girl to CBP, lawyers again presented her at the bridge. CBP did not respond to a question about what changed its calculus, but that afternoon the girl and her mother were admitted to the U.S. D’Cruz, the lawyer, took them to a hotel that night before helping them fly to Louisiana yesterday, where they are staying with relatives and pursuing both medical care and their asylum case. Two newborn babies and a woman with cervical cancer remained in the camp, Perry told me, and though their health was just as precarious, she didn’t know whether she would be able to get them to safety. “In an arbitrary system,” D’Cruz said, “the only way to work is with pressure.”