The alleged driver, Darriean Hess, 19, was arraigned Wednesday on charges of negligent homicide and second-degree assault, the Boston Globe reported.
Later in the day, police said they arrested Cindy Sheppard, 48.
Sheppard allegedly provided drugs to Hess hours before the crash, and then allowed her to drive without a license, police said.
She was charged with selling a controlled substance and allowing an improper person to operate a vehicle.
Sheppard is being held in lieu of $10,000 bail.
The relationship between to the two suspects is unclear, the Globe reported.
Hess was allegedly speeding Saturday when she veered across the road and struck two cyclists who were taking part in a 100-mile ride.
Pamela Wells, 60, and Elise Bouchard, 52, were killed in the crash. Two others were injured, police said.
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