How do you convince someone they're OK when they've convinced themselves they're crap?

I so know this script, it's frightening. A good friend of mine got drunk this evening. I've seen her drink a lot more than she did tonight, and walk home steadily, if merrily. What I didn't know tonight, until it was too late to do anything about it, was that she has just split with her boyfriend. And one's emotions can have such a powerful influence on the effect alcohol has on one. Tonight, the result was that after just 3 glasses of wine, my friend was royally sick, much to her embarrassment and self-disgust. Problem is, the self-disgust was already there, looking for something to hook itself up to.
I so hope she will accept that simply misjudging how much to drink doesn't mean her friends will suddenly decide she's a waste of space and someone they wish they didn't know. That is so far from the truth it would be laughable if it wasn't exactly what she was saying to us tonight. She is someone I admire a lot, and misjudging how much alcohol her system can cope with doesn't change that one bit.
I hope she reads this - maybe them she'll believe what I was saying to her tonight.