My daughter also started her period at 11 (a bit of a shock, as I didn't start mine until I was 14 1/2. But then, my mom told me she'd started at 11 also, so maybe an hereditary thing.)
She was diagnosed at age 12, though I think she may have had it for about 6 months before.
At diagnosis she was at 5k, fluctuating between 3k and 10k for the most part. But, one thing we were lucky with was she never had heavy periods at all. In fact they were very light. When I was a girl (no ITP), my periods were always extremely heavy, so go figure! My daughter is now nearly 20, and has been in remission for 7 years. Her periods are still light.
Just like some ITPers seem to be 'bleeders', sometimes even at fairly high counts, others have very little bleeding even with counts lower than 5k. How is your daughter with other bleeding symptoms? If she does bleed, does she clot quickly?
So, I think it would be wise to wait and see how she's going to do.
And, I can almost guarantee she is not the only one in her class, either, though most of them won't talk about it. I have twins going into the 6th grade, too, and I know that about half of the girls have started, and many appear to be on the verge. There is some thought that the earlier menses may come from all the added growth hormones that wind up in our milk and meat. It's best to look for those that are hormone free. Soy also plays a part, and should be avoided. I would strongly advise against stopping her periods. Many women react very poorly to having their normal menses suppressed. Especially not at the tender age of 11.
april