What is the name of an older movie that has a masked women murder people in a school/church?

I remember growing up [in the 90s] and my parents had this vhs tape, i used to watch it and it would freak the **** out of me. Now i'm trying to remember the name of it, but all I can remember is it taking place in either a catholic school or church, and either a nun or older women puts on a really weird face mask and stabs some people. I just remember it being terrifying when she puts the mask on, stabs someone, and see's someone else on the staircase up above her -and takes off running for them.