She has weathered a storm of conservative critiques for several misstatements, including one reference to 9/11 hijackers traveling through Canada, which is incorrect, and another seeming to dismiss the seriousness of the failures leading to the Christmas Day bomb plot.
"Once the incident occurred, the system worked," Napolitano said on ABC News' "This Week" Dec. 27. The next day she reversed course, saying, "Our system did not work in this instance."
Napolitano has had to apologize to veterans for an agency report that warned some may be particularly prone to right-wing extremism and had to defend her approach to immigration enforcement, which places greater emphasis on the "demand side" of illegal workers.
"I really think her challenge is she's losing the PR race with the American public," said Jena McNeill, homeland security analyst with the conservative Heritage Foundation. "Every appointee is going to make some missteps in things they say. ... I think Janet Napolitano understands completely the threats she is having to work with … but it's really important the person at the helm of DHS is a good communicator."
Still, in spite of the criticism, she has emerged from the first year largely intact, even earning the public support of both her Republican predecessors in the face of recent criticism of her handling of the Christmas Day bombing attempt.
"I heartily endorse her," former Homeland Security Secretary Michael Chertoff told NBC after criticism of Napolitano following the Dec. 25 incident. "[She] has a good skill set."
Tom Ridge, the first Homeland Security chief, called criticism of Napolitano "misplaced."
Observers of Napolitano off the national stage describe a woman who hasn't let the criticism or pressure get to her. "She works; that's what she does. She works all the time," former spokeswoman L'ecuyer said. "The pressure doesn't bother her."
At stake for Napolitano is a career and reputation while faced with seemingly overwhelming odds: The systems Napolitano oversees to keep Americans safe on airplanes, along the borders and even online, need to get it right 100 percent of the time; would-be terrorists only need to be right once, analyst Nelson said.
"If you foil terror attacks, no one ever knows about it hardly," he said. "But if you have one, everybody knows about it" and it's your fault.
ABC News' Jason Ryan contributed to this report.