Redmond-Mercereau, a high school teacher, is also charged with weapons possession and tampering with physical evidence.
Her lawyer, Mario Gallucci, said she denies the allegations completely.
Her husband was found in bed the morning of December 2, 2007, shot three times in the head with his service pistol.
His wife told investigators that she didn't hear the shots because she was wearing earplugs and was sleeping in another room with one of their three children, who was sick.
Prosecutors alleged that she wiped trace evidence off the Smith and Wesson pistol, removed shell casings and washed her clothes to conceal the alleged crime.
"She denies the allegations completely," Gallucci said in a telephone interview Friday. "She is confident that if she is given a fair trial by Staten Islanders, that she will be acquitted of this charge."
His family issued a statement after learning of the indictment.
"We have patiently waited while the NYPD accumulated their evidence and completed their tests. In our hearts, we hope that a fair and just verdict is delivered swiftly, though we know that this too requires patience," the statement said.
Mercereau was a 12-year Fire Department veteran. He and his wife were married 12 years; they had three daughters.
Fire Commissioner Nicholas Scoppetta has called the supervising fire marshal a "rising star within the FDNY's Bureau of Fire Investigation."
