Girl, 9, saved baby. Then dad’s girlfriend tried to kill her and her brother, cops say.

A 9-year-old girl saved her baby sister’s life after she saw her dad’s girlfriend strangling the 6-month-old with her elbow, police said.

The woman, Ailenys Carmenate, 31, later tried to kill the girl and her 12-year-old brother inside their Hialeah home.

The children survived, and Carmenate now faces a slew of charges including premeditated attempted murder and child abuse. She was being held Monday at Miami-Dade’s Turner Guilford Knight Correctional Center with no bond.

According to police, Randy Montano came home Saturday night from work, had a brief argument with Carmenate and then went for a shower. That’s when Carmenate took the baby into the room of Montano’s two older children and locked the door, police said.

She told the kids to get into bed and then put the baby on the edge of the bed. The kids told police they heard Carmenate tell someone on the phone that she had just killed the baby.

The 9-year-old girl “immediately gets up and pulls the defendant’s hair, bites her arms and kicked her, doing everything she can to save [the baby’s] life,” an officer wrote in the arrest report.

Montano heard the commotion and tried to open the bedroom door, but it was locked. The 12-year-old managed to open the door and let his father in, police said.

He tried to get Carmenate — who had switched to using her hands to strangle the baby — off his daughter. The baby fell to the ground, injuring her head, according to the report. Montano fled the apartment with the baby. His son tried to follow, but Carmenate “took hold of his neck and stopped him,” an officer wrote.

The 12-year-old boy was able to escape after she tried to put him in a choke hold, police said. The 9-year-old also tried to escape, but Carmenate “pulled her by the hair back inside and used her hair to violently throw her on the floor,” the officer said.

Carmenate, police said, then tried to choke the 9-year-old.

The girl told police, “she had never experienced a pain like that in her life.“ She said she “thought she was going to die.” She was eventually able to get away, police said.

Montano told police his baby was unconscious when he took her from Carmenate. He was able to revive her, police said.

Carmenate refused to speak to officers and was arrested.