To me, this is just bad management. On all of the floors I've ever worked, nurses would have to submit days that they did not want to work for approval, and no more than 2 nurses could put in for the same day. For long term things like school, medical appointments, etc. it would have to be approved by management. Usually they could accommodate, but at times they could not. To pull a nurse from another shift is the easy way out for the manager, as long as that nurse is not complaining.
It was nice that the op agreed to help out, but management did not keep up their end of the bargain by scheduling her days too close together. I get that anyone can be mandated to work different shifts at management discretion, usually based on seniority but the night nurses should have a more valid reason to not work on Mondays. (Maybe they do and it is being kept private).
I think the op has every right to be upset. Management is taking advantage of her and if they don't resolve it in a fair way, I'd be looking to leave, too.
