"enter vehicle" works (she will path her way over to the car, but only if it is really close to her)... Make sure there are enough path nodes in the area of the car.
"But for some reason, "exit vehicle" doesn't work." ..... The command should target the car with a parameter of "1". Think of it as an ejection seat.
"I also still can't figure out how to get Jessica to follow the player. I'm messing around with "squads" and "teams" to see if somehow that will allow it." ... What you are looking for is "ai_goal_follow". It can be turned on and off.
The biggest problem you are likely to have is when you kick Jessica out of the car. She probably won't know where to go and might stay in the air in her sitting positon.