Well, I suspect that it's just like humans, some girls menstruate at age 10, some not till 16 and a lot in the middle. There may be a problem, but I suspect not likely. But getting her to a vet to get spayed will give you a lot more info.
Holly, Misty & their friend, Jake, the dog.
Onyx, Callie May, Maggie & Kobi forever in my heart.
Yes, I know I need a new signature pic...someday...