Question Author
Thanks for all your replies - I'm surprised to hear that she is not entitled to time off - and I do feel it is very unfair that part-time workers have to make the time up, simply because there are slots available in which they can, where full-timers are given time off with full pay.
However, I'll let her know your replies.
And I only said appointments "can" be difficult to change - when you've waited ages for a date, it's not always a sensible course to turn the appointment down and request another one!