You underestimate the importance of being a friend, of being there, of sitting and listening and of gently urging your friend to get out of the house for a little stroll with you. Mysteria and Sunshine are right in suggesting a counselor or a physician might be of help, and there are some useful self-help books as well for folks with depression, if depression is what's got your friend down.
David Burns, M.D. is a well respected researcher and has written a book or two that a person can use by themselves or with the help of a friend, and it gets at the sort of thinking that makes a person feel stuck and sad. It may not be a depression but some sort of problem with a phobia. You can't really tell without talking with the person with the issue for a while, and what's more important for right now is the sense of hope. Frequently, the sense of treatment being available may be enough to get somebody started to recovery.
Cognitive Therapy is an approach that works with either Depressio or Phobias, and it's usually very effective and is sometimes but not always used with medication. Sit down with your friend and talk some of this stuff over. There are certainly many other options, and the two of you can use talking them over as a way of helping you friend simply talk, period, which is in itself useful. Use the computer and explore together. Ask her what seems to be most interesting or least interesting and why. Be a friend, above all.
Help her into treatment, as Mysteria and Sunshine have said. It's great advice.
You should be able to find some sort of a referral network in your area if you check listings for the American Psychological Asociation, The American Psychiatric Association, or The National Association of Social Workers.