Can I be docked for scheduled days off?

HELP!
I work at a private school in Richmond, VA. My position is the Executive Assistant. I'm salaried and I receive no overtime pay.
Since I work at a school, we have scheduled days off on the school calendar each year. However, this summer I was asked to come into work for two days right before the July 4th holiday weekend (when the school was scheduled to be closed). I was asked to do so the day before I was needed to come in (Wednesday 6/30)... However, because I had already made vacation plans for the Thursday (7/1) and Friday (7/2) before the July 4th holiday, I was unable to come into work.
My boss later told me that I would be docked for not coming in those 2 days because I had not submitted a Paid Days Leave (PDL) Request to her.
My question is: Can she dock me for those 2 days? Even though we have a calendar that designates that those are to be days when the school is closed? Did I have to submit a PDL request to her even though we were scheduled to be out of the office those days?