MIDVALE, UT — Tawny Williams had worried for months that the ex-wife of her daughter's boyfriend would make good on alleged threats made in person and online. Williams got the news she feared on Thanksgiving weekend: Lisa Vilate Williams, 26, was gunned down in front of her boyfriend's twin 3-year-olds as they made homemade Christmas decorations together.

Chelsea Watrous Cook, 32, a high school health teacher, was arrested on suspicion of aggravated murder after the shooting at Travis Cook's home. He wrestled the gun from his ex-wife and pinned her to the wall until police arrived, according to media reports.

Williams died later at a hospital.

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Tawny Williams told The Associated Press that Chelsea Cook had targeted her daughter with bullying on social media, in-person confrontations and harassment for months.

"I worried for her safety every day," her mother said.

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Williams left early from her own family's Thanksgiving celebration in Centennial Park, Arizona, so she could start celebrating with her boyfriend's children.

"I spoke to her an hour or so before it all happened, and she was so excited … to give those kids something happy," Bekah Williams, the victim's sister, told The AP.

The serene picture was shattered the evening on Sunday, Nov. 27, when Chelsea Cook dropped off cold medicine for one of the twins at her ex-husband's apartment building. They met in the parking lot, but Chelsea Cook went inside, according to a Midvale police report.

Chelsea Cook was asked to leave, but refused, and at one point locked herself in the bathroom during a 911 call, then exited, walked to her coat, retrieved a handgun and fired three to five rounds at Williams, police said, according to a Deseret News report.

Their last conversation had been cordial enough, Bekah Williams told The AP. Chelsea Cook had thanked her sister for picking up the twins from day care.

The Cooks' divorce was finalized in January, according to court records. Williams and Travis Cook met at a bank where they both worked, and the harassment started in June, relatives told The AP. Williams was reluctant to report the harassment because she worried about how it might affect the Cook children.

"In hindsight, I think the best thing for the kids would have been to call the police every time," Bekah Williams told The AP.

In October, Chelsea Cook was charged with and pleaded not guilty to domestic violence in the presence of a child in an unrelated case, Bekah Williams told The AP. The slain woman's sister said she reported Cook's behavior to the principal at Skyridge High School in Lehi, where Chelsea Cook worked and the origin of some of the harassing phone calls, but that it didn't feel like her complaint was taken seriously.

The school didn't realize Chelsea Cook had been arrested on suspicion of domestic violence until after Williams' death, Ben Rasmussen, director of law and professional practices with the Utah State School Board, told Independent.

"It took a lot longer than we would hope," Rasmussen said.

Those who knew Chelsea Cook said she was an engaged, well-liked teacher at Skyridge High School, television station KUTV reported.

Kaleb Latimer, a senior who had Chelsea Cook as a teacher and then became her teacher's assistant, told the television station that she had confided in him about her failed marriage.

"Before her divorce, you could tell she was super happy all the time and when she got divorced, she missed a couple days of class, which she never really did, and after that it was just kind of different, I guess," he said.

This undated photo provided by the Salt Lake County Sheriff's Office shows Chelsea Watrous Cook. Police say Cook, a Utah high school teacher, shot and killed her ex-husband's girlfriend while the former couple's children looked on. (Salt Lake County Sheriff's Office via AP)

Tawny Williams wants her daughter to be remembered as she lived rather than by how she died.

"My beautiful Lisa, she was murdered while decorating a Christmas tree with the homemade ornaments she was making with the kids (3-year-old twins)," the grieving mother wrote. "She was so kind, sweet, generous, loving, and brought joy and excitement to every aspect of life.

"Please share the beauty of her life rather than the monster that ripped her from ours. I am asking that anyone that has posted the picture and article with the evil killer as the subject please remove it and share Lisa's beauty instead. She was magic, and I want her remembered for how she lived and not for how she was killed."

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)

The Cook family said through spokeswoman Kimberly Jensen, Travis Cook's aunt, that "no words can express our sorrow over the loss of your daughter, Lisa Vilate Williams."

"She brought great joy to Travis Cook and his children, and her light and beauty will never be forgotten or replaced," Jensen said. "We cannot make sense of this senseless act of violence. We are deeply shocked and saddened. We grieve alongside you during this tragic time."

A GoFundMe account has been established to raise money for a memorial for Williams.

"Lisa was the most amazing and sincere individual," the family wrote. "Everywhere Lisa went, she spread beauty and happiness. She loved all of the small things and was enamored with making every little thing special and beautiful. ...

"We all miss her so much; her spirit was magic and we can only hope to feel it again. … She loved bigger than anyone I know. Our beautiful little sister, daughter, and friend, you are so very loved and missed immensely."

Bekha Williams said her sister "had a wise soul."

"I feel lucky to have had her in our lives," she told The AP.

The Associated Press contributed reporting.

Lead photo: 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)

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