Now Ms. Carr, a speech pathologist who calls herself "a typical American citizen," is as outraged as the girl's teachers and classmates, who have learned that the girl and another 16-year-old are being called would-be suicide bombers and are being held in an immigration detention center in Pennsylvania.

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According to a government document provided to The New York Times by a federal official earlier this week, the Federal Bureau of Investigation has asserted that both girls are "an imminent threat to the security of the United States based on evidence that they plan to be suicide bombers." No evidence was cited, and federal officials will not comment on the case.

Its mysteries deepened as teachers and neighbors gave details of the Guinean girl's life, like the jeans she wore under her Muslim garb, her lively classroom curiosity about topics like Judaism and art and her after-school care for four younger siblings while her parents, illegal immigrants who have lived in the United States since 1990, eked out a living.

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Until now, attention has focused on the other 16-year-old, a Bangladeshi girl reared in Queens who could not deal with the hurly-burly of her West Side high school and withdrew into home schooling. Yesterday, on a motion of the government, an immigration judge closed the Bangladeshi girl's bond hearing to the public and adjourned it to next Thursday, said Troy Mattes, a lawyer who is taking over the case but has yet to meet her.

By the Bangladeshi girl's account, reported by her mother, the girls did not meet until March 24, after their separate arrests in early-morning raids on immigration charges against their parents. Both grew up in Islamic families. But while the Bangladeshi girl had grown increasingly pious, and uncomfortable in the urban culture of the High School of Environmental Studies on West 56th Street, the Guinean girl, a 10th grader, embraced every aspect of Heritage High, at 106th Street and Lexington Avenue, her teachers said.

"She is, yes, an orthodox Muslim, but completely integrated into this school," said Jessica Siegel, her English teacher in a class in which topics like teenage pregnancy and world politics were discussed. Ms. Siegel was profiled in the book "Small Victories," by Samuel G. Freedman, as an unsentimental, but fiercely committed teacher who provoked and delighted her students.

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The English teacher's most vivid recollection was of a day two months ago when she heard a kind of roar in the hallway of the school, which is full of colorful student collages and life-size sculptures in papier-mâché. The teenager had stopped wearing her veil, and she beamed as her fellow students, seeing her face for the first time, cheered.

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Ms. Lane, the art teacher, said that when Heritage High first learned that immigration agents had picked up the girl, one of her best friends asked if someone from the school might have denounced her as an illegal immigrant. "I remember telling her the government doesn't go after 16-year-old girls," Ms. Lane said. "And in the last few days, I'm wrestling with the fact that, yes, it does."