I agree it works really well as a one shot, it is my goto for convention games. Saying that I've played Horror on the Orient Express (1st edition), and Tatters of the King which were both much longer games and it worked out fine. I think the longer campaigns support a slow descent into madness...
Call of Cthulhu is pretty bleak, you character is likely to die or go insane, and the ancient Gods can and do wipe people or entire cities out when the players can't delay them.
Give her a chance, I wouldn't be surprised if she isn't already in the process of applying for citizenship all things considered.
https://www.instagram.com/reel/C3xXYQoISUK/
Problematic content is acceptable even if it isn't obviously and explicitly evil and/or meant to be fought. It just needs to be handled with a little more care, and isn't for every game table. Even then what is problematic is a sliding scale, what is problematic for some tables won't be for...