You mean gluttonous nun, halfbang, Hookbang, protagonist nun, or grey haired? (I think it is gluttonous nun, soo, yeah, we do see her.)
I think they mean the nun on the far left, with the silver bangs. She hasn't appeared very often, and is usually just in the background. She is Sheep nun's mentor as seen on the chalk board in this one: post #4150430 You can see her here next to Star Nun: post #4145666
I second that side-slope-gray nun is a rare one, though we've encountered quite a share of gray-hairs: - Sheep nun, with freckles - kindest nun, Hookbang's roommate. post #4096971 - Smug nun, Scowl's rival. According to mentioned chalkboard - mentor to Glutton nun. post #4105379 - Rabbit nun. Mentor to Hookbang (chalkboard). Hardly changing expressions with her face (those are on rabbit pin/charm).
There's another one "background nun" who occasionally pop up - the one with three thin black strands and freckles. On that chalkboard - Glasses's mentor.
