Police in Berks County said the accident happened at about 10:20 p.m. Monday in Maidencreek Township.
Deputy Coroner Kurt Katzenmoyer said 27-year-old Laura Ringler died shortly after she was taken to Reading Hospital.
A man flown to the hospital was reported in good condition Tuesday.
Northern Berks regional police say the Mennonite couple were riding home after a shopping trip when an SUV struck the vehicle.
Coroner Dennis Hess said the buggy had working head and tail lights, as required by law.
The horse was also severely injured and a police officer euthanized the animal before a veterinarian arrived.