Yes I realise this will be a contraversal idea, but it's an idea to chuck in the pot.

What about the pill? That way she can plan ahead for races and skip a period (or stop all periods) if she wants to or alter it by a few days. There's other benefits as well like lighter periods, can help acne etc.

I wish my mum had helped me ask the doctor to be put on it earlier- the misery of painful and heavy periods while doing an active physical sport (in my case karate- ekk white gis anyone. It was sometimes very embrassing)
and trying to work out whether or not an important event would clash with it.

I realise this also would depend on your personal beliefs on the matter but the pill isn't just for birth control.