Protein shakes typically are based on milk, egg, whey or caseine (milk products), soy, or rice proteins. Since the "leaky gut" which often accompanies chronic candida often causes allergies, some folks become sensitive to milk products, eggs, wheat, and/or soy (and/or other food products). So that's something to keep in mind. But yes, I believe that protein shakes are a great addition to a candida sufferer's diet. Some people freak out about soy, but since I became allergic to milk, egg, and wheat, I took no-sugar soy powder shakes for several months. High-protein foods, and certainly protein shakes, usually contain large amounts of glutamine and cysteine. The former is a primary fuel for repairing the intestional lining, and the latter is a primary anti-toxin, both of which are very helpful in repairing leaky guts and battling candida.
Grains and starchy vegetables are often moderated in a candida diet, but if you are attempting to gain weight (or at least not lose weight), I'd go ahead and include plenty of whole grains and vegetables of your choice and see what happens, modifying later on as necessary. I'd hesitate to say that except I cured myself of candida while consuming plenty of both. The combination of a healthy diet, greatly cutting out sugars, Fluconazole, and herbal meds did the trick for me, although the extra step of eliminating many/most grains and starchy veggies may be required for some others.
Without commenting on same, brown rice, whole oats, and apples all show up in my Immuno Lab's "Candida safe" foods list, as are various potatoes (but usually consumed in moderation).