A former Utah high school health teacher will spend at least 34 years — and possibly the rest of her life — in prison after she shot and killed her ex-husband’s girlfriend.

Chelsea Watrous Cook, 33, went to her ex’s apartment on Nov. 25, 2019, and fatally shot 26-year-old Lisa Vilate Williams in front of Cook’s 3-year-old twins.

In this undated photo provided by Tawny Williams shows Lisa Vilate Williams. The family of a woman killed by her boyfriend's ex-wife while decorating a Christmas tree is sounding a warning about the devastating consequences of domestic violence that goes beyond two people. Police say 26-year-old Lisa Vilate Williams was making homemade ornaments with her boyfriend's twin 3-year-olds when his ex-wife, 32-year-old Chelsea Watrous Cook, burst in and shot her to death in front of the children. (Tawny Williams via AP)

Cook pleaded guilty in February to aggravated murder, aggravated burglary, three firearm-related felonies and two misdemeanor charges of committing a violent offense in front of children.

Third District Judge Douglas Hogan on Monday ordered her to a 25-year-to-life sentence for the aggravated murder, a six-to-life term for aggravated burglary and between three to five years for a firearm charge. He ordered the sentences to run back-to-back to one another.

The judge dismissed two of the firearm charges she had pleaded guilty to, after Cook’s attorney argued that the counts should merge with the aggravated murder charge. He gave her time served for the misdemeanor counts related to her children witnessing the violence.

How much time Cook actually spends behind bars will ultimately be up to the parole board.

Prosecutors allege that Cook had initially gone to her ex-husband’s apartment to give her children cold medicine.

They had texted each other and arranged to meet outside, but when the man went outside, Cook instead went inside, prosecutors wrote. The man returned to find Cook in the living room with Williams and the two children, prosecutors wrote.

After Cook refused to leave, her ex picked up the phone to call 911, and Cook briefly locked herself in a bathroom, prosecutors wrote. She came out of the bathroom and walked toward her coat, prosecutors wrote. Her ex-husband then heard multiple gunshots and saw Cook pointing a gun at Williams, who was fatally shot in the chest, as well as in the leg and hip, prosecutors wrote.

The man grabbed the gun from Cook, who then sat with the children, prosecutors wrote. Cook’s ex-husband tried to call 911 again, but Cook got up and again walked to her coat; the man, worried she had another gun in the coat, pinned her to the wall until police arrived and told the children to go into their room and lock the door, prosecutors wrote.

Cook taught health at Skyridge High School in Lehi.