I had this happen and it really buggered up my schedule. He was a 3pm to 8pm and was always here when I needed to pick-up kids at school or get groceries. What I did was planned a field trip to the zoo on one of his regular days but put on her calendar that I would be closed.
We did a lot of lead up to going, decorating, posted signs, reminders in the newsletters, return your permission slips, etc... Dcm asked why we were going without her child and I told her it was because of her not wanting him to be transported. Told her I felt bad for him and felt that he would continue to be disappointed in the years to come when he got into school and not allowed to go on trips.
Never thought of it like that.