Lynn Marie Maher, 49, of White Plains, was fatally shot in a 7-Eleven in Waldorf, 25 miles south of Washington D.C., the Charles County Sheriff's Office said.
Maher was working as a clerk when a man wearing a surgical mask walked in the store around 1 a.m. and announced a robbery. He demanded money from Maher and shot her before fleeing with an undisclosed amount of cash, authorities said.
She died at the scene. Investigators are still searching for the suspect.
Maher's husband, Travis, took to social media upon hearing about his wife's death.
"She was held up at gunpoint last night, gave the robber everything she could on witness accounts, and had nothing else to give in this persons [sic] eyes other than her valued and loved life," he wrote.
Messages to Travis Maher from Fox News were not immediately returned.
Maher, a mother of four children, and her husband dated as students at Seneca Valley High School in Germantown, WRC-TV reported. The couple later went their separate ways before reconnecting. They got married in Iowa and moved back to Maryland 10 years ago.
"My brother's grieving," Maher's brother-in-law told the news station. "There's so much pain there. It's a senseless, senseless tragic killing."
Maher enjoyed her family and loved teaching Tae Kwon Do, in which she attained the level of black belt, according to news reports.
"She loved teaching the kids," her brother-in-law said. "That was her calling. She just wanted to help the children, help other kids, especially underprivileged kids."