Sometimes a bad case of noro can leave people lactose intolerant for a couple of weeks, she could be having stomach issues from that or she could have something else going on. When I had noro the sickness came on very quickly but I had an idea that I wasn't well hours before hand, I had a terrible headache, I felt very off, my stomach was making a lot of loud gurgling noises (not normal digestion gurgles) and I was very lethargic. The sickness lasted around six hours, the diarrhoea for about 4 then I slept and slept, I felt very weak and unwell the next day and didn't have a normal appetite for at least a week. She really shouldn't be at work and should go to her gp.