My answer (please read my health disclaimer):

As you probably know, I recently went gluten-free, and also greatly reduced soy, refined sugar, and oils. And it's not as tough as it seems, I just have to be creative and appreciate food in it's natural form. I had a great conversation with someone today about how spoiled our palettes are, so much so that we don't like "plain" food and instead prefer it with a ton of salt, oil, and sugar. However, when we remove those additives from our diet we begin to develop a taste for fruits, vegetables, nuts, and seeds in their pure forms.

In the mean time, there are a lot of great transition products available, especially for gluten-free eating. At first, GF pasta (rice, corn, quinoa) with Daiya cheese was my staple, and now that's more of an occasional treat because I'm avoiding oil. Now, I eat a lot of rice, quinoa, beans, and potatoes since they are filling and can easily be made without a lot of oil or salt; I have them with fresh veggies and herbs, and they are delicious. Raw nuts and seeds are also satisfying, but should be had in moderation. I like to keep fruit around so I have something sweet without consuming refined sugar, but if your friend is avoiding sugar all together then those should be avoided (I've noticed that since I stopped eating refined sugar, I don't even want fruit that often). I also suggest drinking herbal teas for flavor (high quality, organic, and fair-trade if possible) - now is a great time to make iced tea (though some sites say all but green tea should be avoided on a yeast-free diet).

As for avoiding yeast, since I've been eating mostly whole foods, I don't usually encounter too much of that. It's usually found in sugar and wheat, so avoiding those foods should make a big difference. I read that alcohol, vinegar, fermented products, and starches like potato and corn may need to be cut out as well.  

You mentioned that your friend is avoiding oats, but I think she can still have them as long as they are labeled gluten-free (easily found in natural markets). There are also gluten-free breads, english muffins, and pizza crusts available: check out Food for Life and Energ-G.

I've found that the macrobiotic diet is quite in line with the way I've been eating recently, except for the soy content. I highly recommend checking out macro cookbooks (like The Kind Diet and The Self-Healing Cookbook), websites, and restaurants.

That's about as far as my knowledge goes on the subjects, so I encourage you to do some further research. Remember that every body is different, so it's important to consult professionals. I recommend seeing a few different doctors to get varied perspectives, and to see some with holistic knowledge if possible. Depending on where your friend is located, I can recommend some great specialists.

Do you have further advice? If so, please add it in the comment section below.

Please send me any questions you have, and they may be featured on EVG! : )