Dear Life,
If you really don't want to tell her in person, then just don't do it that way. I'm reacting to this from personal experience. I was involved with a much younger man, with many mental and addiction problems. In addition to stalking me when I ended it, he used the manipulation of two attempted suicides. I felt "responsible" too. And I also was his only means of financial support at the time.
I know you don't want her to harm herself, but as another said here, SHE is responsible for her own actions. I'm also worried about YOUR safety. Be cautious.
Seeker