From what I understand, girls are developing more quickly today than in years past. There are scientific studies that attribute this to all of the hormones in our foods.
That said, I have to say that a good part of it will also depend on family history. In my family, we have a history of developing early. I started menstruating at the age of 10 as did my mother. It is not to early for her body to be starting to prepare for this. However, I wonder more if it could be attributed to not wiping properly and not cleaning herself properly down below when she is showering (part of which she blamed it on). You might start by explaining to her the importance of proper cleaning in those areas to prevent infection and odor and see if that helps clear it up. Also, you might want to mention it to her doctor at her next checkup/sick visit to make sure that it isn't something that she be checked out further. I really think it is probably just the normal process of growing older and being 9 and not very adept at cleaning oneself when there are other things to do instead. ;)
Good luck. Hope this helps.