Interesting how we will cling to our beliefs when our bodies are screaming for change. It's possible that you can't help this client. Mushrooms are considered problematic by some, and they're not really high protein. Nor is quinoa. It might be high protein for a grain, but it's still 60% starchy carbohydrate. Sea veggies aren't a major protein. Tempeh's good, but she can't eat it every day, and it IS fermented.
Perhaps you can simply point out how Candida develops and steer her towards books and websites that succinctly deliver dietary recommendations that are known to be successful. I really suggest you not spend a lot of time trying to convince someone who is dead set against changing. Takes too much of your energy. Let her get ready first.
Also, if she's vegan for moral and/or political reasons, I suggest you recommend Lierre Keith's book, The Vegetarian Myth to her. In my opinion, one of the most important things we do in life, as adults, is to accept things the way they are. The thinking that veganism is a highly moral way of eating denies what is. That's all I'll say. It's in the book. Of course, she may not be ready for this, either. It'll probably make her angry.
So, this may not have been helpful in the way you're hoping, but I don't think the way out of Candida is with low protein and high starch. You can, of course, suggest vegan protein powders, but this is not a long-term solution. These are not whole foods; they're adjunctive support.
Best of luck.