We can't advise on exact dosages, but we can give general advice and explanations.
Firstly, what type of insulin regime is she on? (Does she have one injection of long acting insulin a day, plus short acting before meals?)
Really, her clinic/doctor should be answering questions like this, or giving her enough information so that she can do the calculations. Diabetes is one of those illnesses where it's best for the patient to understand how to calculate and adjust their own doses. And unfortunately stress does make diabetes control more difficult.
I understand that you want to help her, and that is admirable, but it may also be a good idea for her to come on the forums and ask questions.