I really feel for her as I had the same problem when mine started at about the same age. The first issue is, as PipinHull says, no matter how uncomfortable you feel about it, starting to use tampons would make a world of difference. My Mum really didn't want me too but when I finally did it reduced the uncomfortable 'nappy' feeling as well as made me less self-conscious (gymnastics with a jumbo towel anyone? no, thought not). At that age she'll need help with it though as I struggled to figure it out and make things 'comfortable' on my own.
My GP tried a couple of things that were meant to either reduce the blood flow or reduce the number of periods but none of them worked for me. Ultimately going on the pill at 14 was the solution, even though my parents were very uncomfortable about it. I wish the GP had gone straight to that and saved me a couple of years of hell! Even now it is the only thing that works for me - I'm on a brand that allows me to take three packets in a row so I only have a 'period' about once every 10-12 weeks.