The officer was in the process of picking up the dead animal in the municipality of Ruswil when she was struck head-on by a passenger car, cantonal police said on Tuesday.
The incident occurred at around 9.15 pm, police said.
The policewoman, who was wearing a reflective vest, was thrown to the ground.
She was rushed to hospital for treatment of serious injuries, although they are not life threatening, police said.
The driver of the car, a 79-year Swiss woman, was uninjured in the crash, which occurred in heavy rain.
Police are trying to track down two motorists who were at the scene shortly before the accident to get a clearer picture of what happened.
Schwyz cantonal police, meanwhile, are looking for witnesses after a 92-year-old woman was knocked over and killed by a truck travelling in reverse in Goldau on Monday.
The 39-year-old driver was backing up on a road at around 3 pm on Monday when he struck the elderly pedestrian.
The woman was transported to hospital but died from her injuries on Tuesday, police said.