Asked to work less than contracted hours?

our contracts have a clause included in them to the effect that the company can fix up to 9 days holiday per year- it's to cover shut down periods, but I guess could be used in such a case as the OP.

Your friend could perhaps ask for her case to be reviewed if there are other people who have been chosen to work ... or perhaps see if someone else who is working on that day has holidays left would swap with her ??