It happened around 7 p.m. Wednesday along the 300 block of Winding Hill Drive.
Officials say the woman was walking a dog when a Jeep coasted down a driveway, striking her and trapping her beneath.
Investigators say it appears the key was stuck in the ignition of the Jeep, and in attempt to free it, someone put the vehicle in neutral - causing it to coast.
The woman was trapped for more than 20 minutes, and once freed, was airlifted to Christiana Hospital in critical condition.
There's no word what happened to the dog.
The incident remains under investigation.