Nora Peterson, 34, hit her boyfriend Michael Mielczarek in the head with several different objects during an argument at their Elgin, Chicago home, according to police.
The raining blows caused the 55-year-old to fall and hit his head on the floor, police said.
When Peterson realised that her boyfriend had stopped breathing she called for an ambulance, reported CBS Chicago.
Responding officers found Mielczarek unresponsive and not breathing when they arrived at the apartment at 3.47pm Saturday.
He was transported to the Provena St.Joseph Hospital where he was pronounced dead.
An autopsy on Monday concluded that Mielczarek died of blunt force trauma to the head, the police release said.
Police refused to comment on what the couple had been fighting about.
Peterson was charged on Monday afternoon with one count of first degree murder.
She is appearing in an Elgin court this morning.