I'm honestly mixed on this one.
On the one hand, schoolgirls are great, and she is very pleasing on the eye. Having a traditional Japanese student running around scoping out her enemies with a magnifying glass and whacking them with a briefcase would be pretty cool.
On the other hand, I'm not sure what she does to distinguish herself from other potential characters. I'm not going to play the "she has no moveset potential" card, because we all know Sakurai can make anything work - he made a yoga instructor and a dog / duck duo work, for crying out loud! But I don't think "she's a detective" is enough to warrant her inclusion alone. There are plenty of other potential characters that, quite bluntly, have a more interesting motif than solving mysteries.
I mean, if were going solely by "puzzle-solving detective genius", my vote will always go to Professor Layton (and before the inevitable third-party argument is brought up, it's a hypothetical scenario based solely on that singular element: to wit, that they are both detectives). So I don't think that's really a sufficient argument to validate her as a separate character.
She's also incredibly obscure (I doubt most of us would have heard of her were it not for her Melee trophy), but I'll let that slide. Considering Sakurai specifically expressed interest in her, that's a pretty huge point in her favour. That, and considering the characters I support, it'd be hypocritical of me to suggest that obscurity should be a damning factor.
I don't know. I want to support her, because she does sound interesting, but unless somebody is willing to specifically vindicate her merits to me, I'm going to have to remain neutral.