"She's definitely decided to run," a senior Maloney adviser speaking on condition of anonymity, told The New York Daily News. "She's in it."
Gillibrand was appointed by Gov. David Paterson to fill Sec. of State Hillary Clinton's seat, a move that was coordinated in part by Sen. Chuck Schumer.
Eager to protect his investment of political capital, Schumer in May had President Barack Obama call Long Island Rep. Steve Israel personally and convince him to stay out of the coming race.
But Maloney is undaunted, even by White House chief of staff Rahm Emanuel's recent expression of support for Gillibrand.
"I stand up for what I think is right," Maloney told The News' Editorial Board in May. "I don't think what they're doing now is right - they're trying to push everyone out of the race.
"I've never lost an election," she added. "I don't intend to start now."