That's really sad. I hope she sees the negative effect her thinking has. Depression comes to mind most quickly, but it's really hard to say why someone might have that kind of outlook. I think she can find coping tools in material relating to depression, like CBT, even if that's not exactly her issue.

The trouble is that there's no good way (that I know of) to convince someone that their perception of reality is harming them if they are not open to it.