(I am not any sort of specalist in diabetes)
It’s taken before a main meal because it augments the “natural” reaction to eating and using afterward loses much of the benefit and might destabilise things (that said, there is a once weekly slow release version
manufacturer says you can take it any time within the hour before the meal and there are trial data to back that up
It starts to exert its effect on insulin (& glucagon) release pretty soon after each dose (and I suspect the slowing of gut motility is at least as quick) but levels of the drug can take an hour or more to peak after an injection (no major difference in effect on blood sugars though). There is more effect on the amount people ate if they took it 60 min before meals rather than 30, I think – I wonder if this is what the nurse is getting at.
Of course, there may be something special about your mum’s case that’s leading the nurse to suggest this but I dunno what that might be