It could be a disease related to periods. It's not normal to feel that bad during your period, and could indicate a disease such as Endometriosis. (Which I have.) Endo is actually quite common, afffecting around 5-15% of women. But it's not very well known. She should see a doctor. If you have any more questions feel free to ask.
its just her period, some women have that
Its not uncommon.