Police say an Essex woman used a gun to rob a convenience store in Colchester early Wednesday morning before attempting to do the same shortly after in South Burlington.

Theresa Marking, 22, pleaded not guilty in Vermont Superior Court on Wednesday to charges of assault and robbery with a weapon and attempted assault and robbery. If convicted of the Colchester incident, she faces a minimum sentence of a year and a maximum sentence of 15 years in prison.

Police say Marking brandished a black handgun and forced a cashier at the Colchester Champlain Farms to hand over about $130 from the cash register shortly after midnight on April 10.

The cashier described the woman to police as having blonde hair, standing about 5 feet 9 inches tall and wearing a green jacket with a red hat. Police learned through surveillance footage later showed that she was also wearing gray sweatpants and black combat boots.

When a customer who was in the store approached the counter, the cashier said he can’t help right now because he’s being robbed, court records show. Police say Marking then reached across the counter and grabbed the cash before running out of the store.

The customer told police he followed Marking outside as she left the store and saw her enter a silver/gray Honda Civic, which headed toward Winooski. A nearby Winooski officer who heard reports of the robbery come in over the radio saw the Civic on Main Street and obtained a partial reading of the car’s plate, taking down the letters HEG, court records show.

As detectives investigated the Colchester incident, South Burlington police received a reported attempted robbery in the city. In that case, a female suspect matching the description of the Colchester suspect tried to rob the Champlain Farms along Williston Road, court records show. The clerk refused and the woman left without incident.

A University of Vermont police officer saw a silver Volkswagen Jetta traveling along Shelburne Road shortly after, court records show. Police say the vehicle was silver and occupied by several people, the officer followed it onto Interstate 89 to take a reading of the plate and found it read HEG820.

The officer continued following the vehicle as it pulled into the Price Chopper parking lot off Shelburne Road near Exit 13, at which point Marking exited the vehicle and went into the store. She was arrested and transported to the South Burlington police department.

Police say Marking’s clothing matched that seen on the suspect in the surveillance footage.

Colchester detectives interviewed Marking at the South Burlington station later that morning. She initially denied any knowledge of the robbery, saying she hadn’t ever been in Colchester, but later said she had limited memory of the time period during which the robbery occurred, telling detectives she had been using drugs at the time.

She eventually admitted that she received the weapon from an acquaintance and robbed the store to make good on a $3,000 drug debt one of her friends owed.

Marking was held at the Chittenden County Regional Correctional Facility on lack of $10,000 bail. Her next court date is April 18.