They said it happened at the Malabu Drive Super America as the woman was switching her son places to give him some driving instructions.
Police said the car began to move backwards due to the ice, and it rolled over her leg, trapping her.
A nearby officer was pumping gas and heard the woman crying, so he and some other witnesses rushed over to help.
Investigators said they lifted the car off of the woman so she could pull her leg out.
EMS was called to the scene and reported that she had a broken leg, but is expected to be okay.