As someone who comes from a very religious home myself-a home within which someone can seriously refer to themselves as a "Prayer Warrior" and then get upset when I laugh because "they're fighting against evil spirits and the King of Darkness", I can relate.
It is tricky, because if you express your distaste with the subject, they will assume you must really need to hear it because demons are warping your mind and making you sensitive to the name of God. To someone not suffering from Scrupulosity, I would say simply allow her to share her beliefs as it does no harm. However, if her rants cause you so much discomfort, it obviously is not good for your mental state. I agree with Mr/Miss Rohag in that your mother clearly seems to have issues of her own. Perhaps try to keep some distance for now and focus on recovering. I sincerely hope your mother sees a therapist so that she may discover the root of her obsession with the end of the world as well.