'Double Masked' with a KN95 and an N95 over it...she has to be there for a full shift seeing anyone and everyone...makes good sense. btw, I've tried it myself...the resultant fit is very secure, plus there's a double barrier...not needed when I'm only in store for a few minutes, but for her, it's a wise decision.
One thing for sure...not wearing a mask offers zero protection...no doctor or nurse would dare not wear one in an environment that had the possibility of COVID circulating...plus they'd end up being fired if they didn't.
It's not that hard to figure out what to do...but if you're having trouble, check out the attached link.
Link: https://www.health.com/condition/infectious-diseases/coronavirus/why-you-should-wear-a-mask