The school’s first duty is to the children they serve. The teacher’s personal situation presents a threat. Her job security cannot come before that.
That said, the Catholic church should offer to arrange a secret relocation to a new diocese and teaching job, preferably with new identities.
And the twit should buy a gun, she is not safe.
Then let the school hire armed guards. It’s not her fault her ex-husband is a nutbar.
This is one of the very valid reasons for CCW on school campuses.