Ohhhh. I see the problem. He is going to end up working both T-day and over Christmas? I see why the aggravation and venting. I would be a bit miffed too. Did he remind her that he had the time off on the calendar for 7 months?
if it's a union job and he's been promoted then he likely lost all rights to the vacation that was preapproved unless he negotiated it before promoting. it's pretty common in union contracts that once you have a new job classification, even if it's in the same work unit, your pre-existing vacation approvals don't travel to the new position.