A Utah teacher is accused of shooting and killing her ex-husband's girlfriend in front of the former couple's children.Thirty-two-year-old Chelsea Cook is charged with first degree aggravated murder.Police say the high school health teacher went to her former husband's suburban Salt Lake City apartment to deliver cold medicine to one of their 3-year-old twins Sunday night.They say there was an altercation. Cook was asked to leave, but refused.Documents say Cook pulled out a handgun and fired three to five rounds at 26-year-old Lisa Williams. Williams died at a hospital.The shooting took place in front of the 3-year-old twins, police say.Cook was charged with first-degree aggravated murder.------