It is very hard to control those feelings, when you are worried about a close friend. I just went through a four day period in a fog, thinking that my friend had done something truly awful. In the end, he was all right and I was annoyed with myself for worrying.

I think you have to assume that your friend is okay, even when you don't hear from her. It's really common not to hear from people who aren't well. However much you worry has no effect on your friend, for good or bad.

Could you establish some sort of relationship with someone who sees your friend on a regular basis, a family member of hers, maybe? Someone who could tell you that your friend is okay?