The shooting occurred about 3 p.m. Wednesday. Two Loudoun County deputies had been called to respond to a disorderly conduct complaint at the Sterling-area Costco. Police said the woman was threatening store employees.
Officials say the deputies ordered the woman to drop the weapons, but she advanced on them. Authorities say one deputy used a stun gun on the woman, but it was ineffective.
Police say the second deputy fired several shots, killing the woman. She was identified as 38-year-old Mhai Scott of Sterling.
Authorities say Scott worked for Club Demonstration Services, which provides services to Costco. The Washington Post reports Scott had been serving pizza.
One deputy was injured. He was treated and released at a local hospital.
See police press conference below: