Numbers 12 is interesting on a number of levels, but I'm dealing here with the relationship of Miriam's sudden leprosy and the shining of glory.
First, leprosy in the Bible is not modern leprosy, known technically as Hansen's disease. Googling leprosy for modern experience is not really helpful.
In chapter 12, Miriam and Aaron had challenged Moses' authority. Specifically, they challenged Moses as a unique speaker for God. God descends in a cloud, and verifies Moses' authority, and when the cloud ascends, Aaron sees that Miriam is leprous.
Note the contrasts: God speaks in "dark" speeches (vs. 8) while Miriam becomes "white" (vs. 10). Also note that the proximate cause of the rebellion is Moses' marriage to an "Ethiopian" woman, presumably a woman of darker skin. (Another note: "Ethiopian" in the scriptures is a term meaning anyone from sub-Saharan Africa. It doesn't mean the modern political entity of Ethiopia, although it doesn't exclude people from that region).
The face is where the glory shines. Miriam's face becomes inglorious, even worse than if her father had spit on her face. She is shut out of the camp for 7 days for uncleanness and the people wait on her to begin their journey again.