I would take her to the Dr. Not to startle you but I would be more concerned that it was something else. The period would be the least of my concerns. As I said not to startle you but I would be going to the Dr ASAP. I would have also kept the nickers unwashed... but I'm also a bit paranoid.
yep this was my 1st thought too sorry to say...

I have heard of the chicken thing too, but 7 seems very young to me, even if you eat heaps of chicken...

than again if all you family got AF quite young ( 11 is young too me I was a late bloomer 16 )then maybe the next genaration is going to start even younger...

the best thing you can do is breath and make her a doctor appointment asap, too see whats going on...

keep us up dated, I will that is nothing more serious