Am I Wrong? in I Need A New Job

When I became manager a few things changed. One of those things is that I actually post a shift calendar. I told all the employees that when they need to switch shifts (one here and there), or they just get someone to cover for them, they don’t need to approve everything through me provided it doesn’t do anything funny like put others into over time. What I did was I asked that they make sure to record it on the shift calendar for future reference.
On top of that I told them that if they needed extended time off, that is what needs to come through me in the form of a vacation time off request: I need to approve anything over 2 days.

I came into work on Monday and noticed a ‘note’ left for me from one of the girls simply stating that she’ll be away May 12-21st. During that time she’ll only be missing 3 shifts and already asked one of the other girls to cover two of them.

So when I saw her the next day, I told her it was unacceptable. I don’t expect her to know ahead of time all the time off that other people had asked for, but for the dates she just told me she would be away they were already booked off by another person. You cannot just assume you can have 10 days off. Her response was (of course) “I only asked for 3 days off”, to which I responded that she is away for 10 days which means she is unavailable to the company for those days, therefore it needs to be approved. Especially since if one person is away, there is a good chance she would be scheduled to cover shifts.

I informed her that I am able to schedule her time off (some days I don’t know how), but in future if she does this again it is a hard no.

So I really don’t feel like I’m in the wrong here, but there is something nagging me about it.