The incident occurred in the municipality of Unterägeri shortly after 11am, Zug cantonal police said.
The motorist drove into a parking lot in front of the vet’s office and instead of applying the brake hit the gas pedal propelling her vehicle against another car before smashing through the front window of the office, police said in a statement.
A 58-year-old woman and a 61-year-old man in the office were slightly injured, according to the statement.
The driver of the car escaped injury although she suffered from fright, police said.
Officers asked the octogenarian to relinquish her driving permit on the spot.