Visiting Houston last week to lead a four-night revival for a local church, Ms. Ukpabio, 41, had no idea that “Saving Africa’s Witch Children,” which brought protesters out to greet her in London, was about to be shown in the United States. But she was eager to defend herself.

“Do you think Harry Potter is real?” Ms. Ukpabio asked me angrily, in the lobby of the Holiday Inn Express where she was staying. “It is only because I am African,” she said, that people who understand that J. K. Rowling writes fiction would take literally Ms. Ukpabio’s filmic depictions of possessed children, gathering by moonlight to devour human flesh.

Still, “Saving Africa’s Witch Children” makes clear that many rural Nigerians do take her film seriously. And in her sermons, Ms. Ukpabio is emphatic that children can be possessed, and that with her God-given “powers of discernment,” she can spot such a child. Belief in possession is especially common among Pentecostals in Nigeria, where it reinforces native traditions that spirits are real and intervene in human affairs.

In Nigeria, many preachers not only identify possessed children but charge dearly to perform exorcisms. To redeem their children’s souls — and to keep the child from being killed or banished by neighbors — parents scrimp or borrow to pay the preacher.

Ms. Ukpabio argued that “Saving Africa’s Witch Children” exaggerates or invents the problem of child abandonment. Asked how she could be so sure, she said, “because I am an African!” In Africa, she said, “family ties are too strong to have a child on the street.”