actually...this may not be a popular opinion here...but I used to work for OBGYN docs for many years...and the BC pill thing is really a very good suggestion. She could be prescribed a very low, low dose pill and she can take them for 3 months...have a period...take them for 3 months...have a period...you get the picture...this way you can "plan" for them. It is my understanding that there is nothing physically wrong with not having your period. Otherwise, it would not be recommended for women by doctors without some serious research. The doc's I worked for stated that you could only have it once a year if you wanted. I am just thinking that you could try this until she is a little older and able to grasp what is happening to her body. It's just a way you could "plan" when she will have them. I know this won't be a choice for everyone...I just think you might want to consider talking to an OBGYN doc.
Thanks for posting this...my dd is 3 and I know that one day, I am going to be in the exact same shoes you are right now. It gives me something else to think about