Maikou
Smash Ace
Well, the N64 Castlevania games seem to be kind of obscure compared to the rest of the franchise. Plus, the protagonists of the games don't have as much uniqueness in terms of moveset potential as a lot of other Castlevania Protagonists do. They've all only got two basic attacks, and their sub-weapons are the same as every Belmont's. (The axes, the Holy Water, daggers, Crosserangs, etc.)Where was all of this Carrie support before?
That said, I support Carrie and Cornell because they both have unique aspects. Carrie wields a pair of ring-shaped blades alongside her magic, and Cornell's not only appeared in Castlevania Judgement, but also was apparently designed as a "close-range martial arts character", so besides his claws and the odd claw beams he can use in Legacy of Darkness, he's not hard to make up moves for. Carrie's a bit more difficult to do because she's 12 and only uses a simple homing shot as her magic attack, but she has potential and it'd be cool to have an explicitly pre-teen girl slaying gods in Smash.
Most of Smash's kid characters are boys, and Pichu's gender is ambiguous. The Ice Climbers and female Villagers might count, but they also might not, it's hard to tell how old they are. I think the female Pokemon Trainer/Leaf is the only explicitly pre-teen girl on the roster, and she hangs out in the background like the male/Red while she directs her Pokemon.