A Texas woman was fatally shot in a Dallas parking lot after an argument allegedly sparked by a lack of gratitude for a small gesture, police say. Cecilia Simpson, 41, was killed outside a PetSmart store on Tuesday afternoon, moments after a confrontation with 22-year-old Keona Zachyua Hampton escalated into violence, according to Dallas police and witness statements.

The dispute reportedly began at a nearby Five Below store in the same shopping plaza, where Simpson held the door open for Hampton. When Hampton didn’t thank her, Simpson allegedly became irritated, and the two exchanged words.

Simpson and her teenage daughter then drove to PetSmart. Inside, Simpson told employees she believed they were being followed by Hampton. Police say Hampton entered the store shortly after, argued with Simpson’s daughter, left briefly, then returned and reignited the confrontation with Simpson.

After being asked to leave by employees, Hampton allegedly threw a bottle at Simpson’s car. A physical altercation followed in the parking lot, during which Hampton reportedly pulled out a handgun and shot Simpson three times.

An ER nurse who witnessed the shooting told FOX 4 that Simpson and her daughter tried to get into their car to avoid the confrontation, but Hampton kept pushing for a fight.

“The shooter was saying, ‘Come outside. Let’s handle this outside.’ The mom and daughter were just telling her to go away,” the nurse said. “They started to fight, and that’s when the lady pulled out her gun and shot her.”

The nurse administered CPR until paramedics arrived, but Simpson died from her injuries.

“The daughter was next to the mom the whole time. The screaming of a child for her mother is never easy,” the nurse added. “It’s never going to leave my head.”

Hampton was arrested later that evening during a traffic stop. She admitted to arguing with Simpson and claimed she only drew her weapon after the situation became physical. She has been charged with murder and remains in custody without bail.