She is naturally a brunette so she wouldn't have blonde hair at all. The only reason she had blond hair was because of the magic flower and I am also assuming that her hair grew so long so fast was also because of the magic flower. (No ones hair grows to be 70ft long in 18 years it just doesn't happen) but if she never cut her hair she could reasonably have tailbone or knee length hair but I don't see why she would have blond hair.
I disagree. Blond hair, that was because the hair had power in it. I don't think she's naturally blond (I'd have to watch the movie again to see her in baby form, but I'm pretty sure she's brunette). Though long hair, I think that'd make sense. Just not extremely long, maybe up to her butt or higher would make sense. At least, to me.