when you say there are shifts to her working, how do you mean?
early and late starting?
if so, what you need to do is get her used to getting up and then having something to eat within the first hour
so if she gets up at 5am she should eat soemthng like a bit of taost by 6, but if she's working late and she can get up at 11am, she should aim to eat that same bit of taost before 12
and then carry on throughout the day

the only problem with this i find is that your body still wants to go for a dump at the same times, so if youget used to having a poo at midday its fine if you are on lates, but if you are on earlies it's a bit incovnient having a crap at work or having to rush home

trial and error really until she finds what suits her best and then, with some variation she can see what effects her when she changes from a set routine, but you've got to find out what works for her first before there is any changing to the set up