A sadistic Queens woman who beat her 1-year-old daughter to death and seriously injured her twin brother pleaded guilty to manslaughter and assault on Thursday, prosecutors said.

Tina Torabi, 30, was arrested for assault soon after police found her daughter, Elaina, beaten to death in her Auburndale home on Oct. 3.

On Thursday, prosecutors slapped her with the second-degree manslaughter charge on top of the assault charge and secured a guilty plea from her.

She faces up to 12 years in jail when she is sentenced on May 30, prosecutors said.

“The expected sentence of the Court is just and punishes the defendant — giving her ample time to dwell on the failures that led to her own child’s death and the other baby’s suffering,” Acting Queens District Attorney John Ryan said.

When cops responded to the house in October, they found Elania Torabi with bruises to her head and genitals, a large wound on her abdomen and blisters and open lesions across her body, police sources told The Post at the time

The toddler’s twin brother, Keon, suffered equally horrific injuries, such as broken ribs, bruises on his groin, a broken hip and lacerated liver, but managed to survive.

Her three other children — ages 5, 4 and 2 — were found living in squalor in a filthy basement, prosecutors said.