Those are her thoughts, almost exactly.
My powers are strong today
I think I understand how she perceives the world, but I'm not sure what the solution is.
With the words of reassurance that I suggested up thread, as well as finding ways in which she's a good omen, here are some more thoughts...
I get the impression that she has some wrong priorities. The thing with the mirror whispering and the prom and being bothered about not being kissed sound reminiscent of people who believe they won't be complete until they get married, as if achieving these things is necessary for their self esteem.
I think her focus needs to be drawn away from those goals, because as long as she dwells on these thoughts, her situation will be self-seeding.
I think she needs to look for happiness outside of school, and care less about what the people at school say and do. She may need a helping hand to do that.
For example, have you done makeup evenings with her? Definitely not to try and impress her peers, just for fun and giggles between you two in private. It may help to boost her self esteem.
Or if she enjoys her food, then teach her how to cook, (or more discretely, asking her to help you while you learn to cook) and she can feel proud of that and build up her self esteem with practical adult skills.
If she does believe in good/bad luck, then add an optimistic slant to that by dropping comments discretely into conversation, such as "you were lucky to get that." Playing games of chance may also help her to see luck from a more realistic perspective.