If you were certain it were a yeast infection, boric acid capsules are sometimes suggested (used as suppositories), but I've never heard of pouring boric acid powder directly onto the vaginal skin. Boric acid is used to treat various kinds of body yeast, but usually not on areas as tender as 'directly on her clit.' If the two of you are sure she is dealing with a yeast infection, she might sit in a sitzbath with boric acid mixed in, or use the capsules, but it just seems like what you are doing is pretty harsh. Also, boric acid can disrupt the endocrine system if used too much. And, since you don't know what is causing the spots, you might be doing it for nothing.
There are a lot of reasons someone might have little white dots in the vaginal area. Have you or she googled the question? I found an article that referenced a dozen possibilities, from shaving irritation to STDs to cancer.
If I were your wife, I'd see if there was a local ob/gyn who is taking new clients, and go for an exam and just pay cash. She doesn't need to keep going there, but if she can't get in to see a doc using her regular insurance, she would at least be able to get a diagnosis.