Healdsburg police Sgt. Matt Jenkins said Sheyna Douprea, 23, was arrested at about 5:20 p.m. after she was questioned at police headquarters following the killing.
Police responded to a home on Mason Street at 12:33 p.m. after receiving a call from Douprea's mother, who was not at the residence, Jenkins said.
They arrived to find the victim, Daniel Gerard Mooney, suffering from life-threatening injuries.
He was taken to Healdsburg District Hospital where he was pronounced dead at 1:10 p.m., Jenkins said.
Police are not yet disclosing how Mooney died. An autopsy is scheduled for Tuesday, Jenkins said.
Police had responded to the home twice previously for incidents not related to domestic violence but did not arrest anyone, Jenkins said.
Douprea is being held under no bail in the Sonoma County jail and will be arraigned Tuesday morning in Sonoma County Superior Court.