How do I help my depressed friend?

Talk to her. I don't mean sit her down and have a long conversation about this. That might not be a bad idea, but there's a sneakier and potentially more effective way to go about it. Mention things here and there, seemingly at random and rather frequently. Tell her how awesome her hair looks today and what is she doing to avoid frizz in this weather, etc. Silly little things like that will build her confidence in her appearance. Include her whenever you spend time with your friends, ask her advise about things, try to "get into" something that she likes that you might not. If she feels like she's wanted and has something to contribute, she'll feel better about herself as a person.