Menstrual cramps are normal to have and I get severe menstrual cramps on the first day of my period as well. Typically it is just from hormones that causes the cramping, as the surge will cause contractions, making her period painful. Prevention is much better than management for pain. Exercise and eating healthy can help prevent menstrual cramps to a certain point, but won't always get rid of them. If she does use pain medication, make sure she takes it at the absolute first sign of pain/cramping because if she waits until the pain is bad, it's already too late for the medication to be effective. Avoiding caffeine can help, along with using a heating pad or taking a warm bath. If the pain does not respond to all of the above, then make a doctor's appointment to talk about better ways of handling the pain. Hope it all goes well.
Is it just the first day? Does she get it any other time even if its not as severe? When did she get her first period? Does she take aleve or advil to relieve the pain?