Kim Taylor, 73, was attacked by the comfort animal at Cultivate Care Farms in Bolton, west of Boston, on Saturday morning.
Taylor, who had been a volunteer at the therapy farm for just over a year, was in the pen alone with the sheep when it charged at her, NBC10 reported.
She suffered extensive injuries and went into cardiac arrest soon after first responders arrived.
The volunteer was pronounced dead after being rushed to the hospital.
Police said all animals at the farm are comfort animals.
The farm, which describes itself as one of the premier farm-based therapy outpatient programs in the country, said it was devastated by Taylor’s death.