The family of a woman who authorities say was killed by her boyfriend's ex-wife while decorating a Christmas tree is sounding a warning about the devastating impact of domestic violence that goes beyond two people.

Lisa Vilate Williams, 26, was making homemade ornaments with her boyfriend's twin 3-year-olds at his apartment on Sunday when his ex-wife, Chelsea Watrous Cook, 32, burst in and shot her to death in front of the children, police said.

The slaying came after Cook targeted Williams with online bullying, in-person confrontations and harassment for months, her sister and mother told The Associated Press.

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

Chelsea Cook's lawyer did not return calls seeking comment, and family members reached by phone declined to comment or did not return messages. She was arrested on suspicion of aggravated murder after her ex-husband took the gun away and pinned her to the wall until police arrived, authorities said.

Lisa Williams died at a hospital.

She had loved reading books and buying dying plants to nurse back to health. On her 16th birthday, she saved money to buy gifts for everyone in her family, said her sister Bekah Williams. She loved children and was so eager to begin Christmas decorating with her boyfriend's twins that she left early from her own family's Thanksgiving celebration in Centennial Park, Arizona, with a popcorn popper strapped into the back seat of her car.

"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 said.

But during the six months she dated Travis Cook, a colleague at the bank where she was a teller, she had allegedly been targeted by his ex-wife. The harassment started in June and included confrontations at the bank, bullying on Instagram and phone calls made from the high school where Chelsea Cook was a health teacher, Bekah Williams said.

Court records show the couple's divorce was finalized in January, but Chelsea Cook had been charged with domestic violence in the presence of a child the month before the slaying. She pleaded not guilty.

Chelsea Cook's lawyer in that case did not return calls seeking comment, and family members reached by phone declined to comment or did not return messages.

Bekah Williams said she reported the behavior and use of school phones to the principal at Skyridge High School in Lehi in August, but "it seems to me that nothing was done," she said.

Alpine School District did not return messages seeking comment on Friday, but Ben Rasmussen, director of law and professional practices with the Utah State School Board, said teacher behavior outside the classroom can be difficult for schools to address.

School officials also weren't aware that Chelsea Cook had been arrested Oct. 16 on suspicion of domestic violence. While teachers are required to self-report such arrests to their superintendents within 48 hours, she hadn't done so, Rasmussen said. The state also flags arrested teachers though a fingerprint database, but it was a misdemeanor case and her prints weren't flagged for more than a month. The notification came through after her murder arrest.

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

At school, meanwhile, Chelsea Cook was an engaging teacher whose class students looked forward to attending, KUTV in Salt Lake City reported.

Details of the domestic violence arrest haven't been made public, but Bekah Williams said it didn't involve her sister.

Lisa Williams was reluctant to report Chelsea Cook's behavior to police, worried that involving authorities could make the situation harder on the children, her sister said. Looking back now, she wondered if that was a mistake.

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

She's at a loss to explain exactly what led to it. The last conversation between the two women had been encouraging, with Chelsea Cook thanking Lisa Williams for picking up the twins at day care. They hadn't had contact in the days before, since she was with her family for the Thanksgiving holiday.

Lisa Williams had moved to American Fork, south of Salt Lake City, a few years ago to care for her sister, who was hospitalized with a potentially life-threatening lung ailment. She'd stayed after the recovery, living with two of her sisters.

In the end, it's that kind of caring for others that Lisa Williams' family hopes she is remembered for.

"She had a wise soul," Bekah Williams said. "I feel lucky to have had her in our lives."