Or HaChaim on Numbers 12:10/אור החיים על במדבר י״ב:י׳

1 והנה מצרעת, and here she was afflicted with Tzoraat. There was no need to repeat this seeing the Torah had already mentioned it in the first half of our verse. According to Sifri who claims that Aaron too had been afflicted the repetition could mean that whereas Aaron had already been cured Miriam continued to be afflicted. According to Sifri Aaron's affliction disappeared as soon as he turned towards Miriam. Accordingly, we would have to assume that Moses had not been looking at Miriam at all. Why else would he have to be informed by Aaron of her affliction before he would pray for her?