What a Person In Pain Really Needs
Of course, there's some "help" they don't need. Rousing statements—"Don't let yourself get upset about this," "It's not a big deal; put things into perspective"—are just frustrating. Shoulds—"You should try harder," "You should be over this by now"—absolutely do not work; telling people how they should feel rarely makes them feel better. Most people are trying their best to do so—the reason they can't is because they haven't yet figured out how. That's not a failure on their part. If someone is struggling emotionally, we seem to believe she's not a strong person. But the two are unrelated. Completely.
Anything you can say to remind her of that is good. As is conveying that she no longer has to live with this level of distress. Say, "I care about you, about what happens to you; I want to be here in a way that's helpful." People with mental illness have this fear: If they knew how bad I am, they wouldn't want to be close to me. However you can, communicate that you understand that emotional issues are part of the human condition, that you don't think any less of her. That's what's truly helpful.