A 20-year-old Colorado Springs woman pleaded guilty Friday to second-degree murder, admitting to brutally slaying her mother-in-law after hearing "voices" in her head.

Under a plea deal with prosecutors, Ellyzabeth Joy Rainey faces 40 to 48 years in prison at her April 4 sentencing by 4th Judicial District Judge Barbara Hughes.

Defense attorneys previously argued that Rainey was mentally disturbed and didn't have a "culpable mental state" the day she dumped boiling water on Deborah Rainey last April and before stabbing her, bludgeoning her with free weights and pouring bleach into her mouth.

Deborah Rainey, of San Francisco, had been visiting Rainey and her husband to help care for their newborn child.

Rainey told police afterward that "voices" told her that her mother-in law-was "trying to take everything away from her." The woman had been previously diagnosed with bipolar disorder.