Totally flat with nothing at all? No, definitely not. She'll develop some boobs, although they could be anything from so small you can't tell they're there unless she's naked or in a swimsuit to huge. I don't think we know when Kaede's boobs came in, so it's quite possible she'll be like Kaede in high school.
It's not at all unusual for middle school girls in the US even to be flat or nearly flat. Hell, I saw a 14yo girl who was once. (That's ninth grade, first year of high school.) And since Asian girls tend to have smaller breasts in general, it's even less unusual there.