She is maybe less crazy than she seems. Just maybe. If you can inflate bike tires with CO2 cartridges, you can do the same with a car tire. Doesn't mean you should, especially at a gas station, where you can get it done in a more conventional way.
I actually saw a video of two guys from Poland destroying tires with two types of extinguishers - powder and plain CO2 https://www.youtube.com/watch?v=0yfXYOyZXEs
I don't see how CO2 can hurt the rubber in any way actually. But if she is using a powder extinguisher, which I doubt, she needs to replace the tires ASAP.
She is lucky it didn't blow in her hands though. Handling condensed gases like that is dangerous.