I can speak to this. I have personal experience. I lopped off over 10 inches of hair and it was one of the most liberating feelings ever. Not to mention I had a great fucking hairdo. BUT! It goes way beyond what you think. She must take into account what type of hair she has, is it thick, fine, coarse, wavy, straight. etc. Some hair types simply look drab when they are cut short because thin or fine straight hair will not take to any style. Longer hair is better in this situation. If however, her hair is thick, and wavy perhaps, then a short hairstyle will likely look better.
people have very distinct opinions about this though. its either love it or hate it. either way, if you do cut it, and you dont like it, at least you know it will grow back.
BM should also weight in, as she cut the dickens out of her hair also. And she looked fab!