Well, I've been in a similar situation, and it has turned out that the person was lying about what they had to get attention...

So, this might be bad advice, but I'd leave and not talk to her, a lot of people come up with them having a terminal illness to get attention or perhaps a way of trying to break up, so I'd be careful.

But, if you really like her, stay with her. If you're not crazy about her, just leave it, be a friend if you want and help her but don't interfere to much about it unless you know for sure she has this.