Job sharing and bank hols?

I job share and always work mondays so when I got someone to jobshare she wanted to share the bank holidays, but I don't think the current system is fair as when its my BH I simply work a day less (i.e not the Monday) but when its her BH I end up working one day more so she gets a day off OR she holds on to it til it suits her...could someone tell me in Ireland what the proper system should be? thanks PS she wont' change days around so that she works the start of the week every second week....