This sounds like an awesome scene.
First question, what type of power does she have (if she does have one)?
Second question, is the car on its side? up side down? Uh, did it land on its wheels so it’s well, landed how cars should be?
Third question, is the mutant coming at her? Or does she have time to get the gas? If the mutant is coming at her, is there someone there to give her time to get the gas?
Fourth question, what does she have on her? Just her clothes? A phone? Maybe magic rope? (okay maybe not that but still). You said that she just got off her normal job so is she taking anything from the normal job she could use to help with the gas idea?
Fifth question, what is this story because it sounds awesome and I kinda wanna read it now.
It depends on how the answers to my questions are. If she’s alone, it would be better for you to make it so the car is on it’s side and the gas is leaking out or the tank at least has a hole into it. This would let her find a way to use the gas quicker then if she has to put a hose into the, place a gas thing goes.
If the car is leaking (rather it upside or on its side) she could trick the mutant to head towards it and throw a match/lighter/uh something that causes fire at the gas on the ground. But that always depends on the type of character you have and if she cares about anyone who might be around. If this is at night/day and no one is around but her and the mutant, then I suggest just blowing the car up.
Kinda sounds fun… For a story.
Another way to use gas from a car is to have the thrown car (or any car it crashed into) to have a gas can that has some gas in it. If she doesn’t have some super skill that allows her to carry car tanks, that’s a good idea as well. (I would drive around with one sometimes, so that is something people would do). The gas can would be easy to carry and if it has a cap, a good way to throw gas at the mutant.