VIENNA, Va.—Four years ago, on a truck barreling toward the forest hideout of Boko Haram, teenager Kauna Bitrus made a desperate move to avoid the fate of the more than 200 other schoolgirls abducted from Chibok, Nigeria, that day.

She jumped.

When Kauna landed, months later, in the pine-shaded town of Grundy, Va., she was among the lucky...