The fire in the northeast Arkansas Wal-Mart was set around 8:30 p.m. Thursday, which prompted an evacuation of the store.
According to the Blytheville Police Department, the fire marshal interviewed McGee on a tip and she confessed.
McGee was then taken to the police station, where she made a formal statement. She was arrested and charged with arson.
Fire and police officials say Wal-Mart suffered almost $100,000 worth of fire, smoke and water damage.
No injuries were reported.
McGee's bond is set at $1,000.