She came in with the infection.
Via NY Post:
The 7-year-old migrant girl from Guatemala who died while detained by the US Border Patrol succumbed to a bacterial infection, according to an autopsy released Friday.
Jakelin Caal Maquin died on Dec. 8, a day after she and her father crossed the US border into a remote part of New Mexico in a group of 163 migrants.
She was the second child to die in Border Patrol custody in December, which sparked questions about the agency’s ability to deal with migrant families.
When they were apprehended by Border Patrol at about 9:15 p.m., her father signed an English-language form saying the girl was in good health, but it’s not known if he understood the paper.