A mother accused in the death of her 4-year-old son, who fell 75 feet into the Willamette River along with his older sister, has a history of domestic violence and recently filed for separation from the children's father, police said.

Amanda Jo Stott-Smith, 31, was taken into custody at a downtown parking garage Saturday morning — some six hours after her children's screams were first heard on the river.

She had threatened to jump off a ledge when officers arrived, police said.

A state medical examiner determined that Stott-Smith's son, Eldon Jay Rebhan Smith, drowned. Her 7-year-old daughter was hospitalized after surviving more than a half-hour in the cold water. Police said Sunday afternoon that the girl's condition was improving and she had spoken with officers.

"How she's not dead is a miracle," said Sgt. Mike Marshman, a Portland Police Bureau spokesman.

Stott-Smith faces aggravated murder and attempted aggravated murder charges. She is to be arraigned Tuesday afternoon.

Police have not yet released a motive. It's unclear if the woman has an attorney.

Stott-Smith filed for separation from her husband, Jason Smith, in March, according to Washington County Circuit Court records. The parents had joint custody of the children, Marshman said.

Court records show Stott-Smith had been charged with domestic assault in 2000.

Early Saturday, the father filed a missing persons case. The report filed in suburban Tualatin helped authorities identify the children, police said.