Well yeah, if she ended up stopped in a travel lane, and got hit, it somewhat is her fault. Pull off to the shoulder with the momentum you already have…. (And don’t try limping an unreliable car onto the freeway either- that might be an issue as well, or maybe not). It is generally not legal, nor smart, to just stop in the road, except for an actual emergency, and an engine stalling really isn’t an emergency by itself, because you should be pulling off onto the shoulder.
If she was on the shoulder, with her hazards going, then I would say she is not at fault.
Now if there is no shoulder anywhere, well this is where not taking an unreliable vehicle onto the freeway might come in. Whether she had her hazards on matters as well.
Anyhow- just deal with the insurance companies, such is life. I know of people who were killed in circumstances like stalling out on the freeway in the travel lane, so she got lucky if she did not get hurt.
<——- crash investigator. But this is pretty minor it sounds like, so someone like me probably did not/will not be involved.