BELIEVE!
Seriously though she would be a great addition, sadly it will never happen. SSB needs more female characters and more characters that dont just use their fists or a sword. There are other weapons out there Sakurai, axes, lances, staves, knives, clubs, etc.
This lack of diversity is especially apparent when you look at how 4 of the current 18 characters in Brawl do not rely on unarmed combat and as well only 4 of the 25 Melee characters did not either, of which all 4 use swords in both games(though Pit does use a bow too). There is a desperate need for armed, non-sword users in the series.
I completely understand the series is supposed to be top Nintendo characters clashing against each other, but its also now become a premier fighter and should not be crippled by the need for every character to be a complete superstar in order to appear in the roster. Characters like Nephenee, Titania or Lyn should not be sidelined because they arent recognizable enough when they offer a unique characteristic to the game.
I didnt know anything about Marth or Roy when I first unlocked them in Melee, but I looked them up, I read their profiles, and because of that I got interested FE in the first place. Same for Ness in the original SSB, without whom I never would have gone back and played Earthbound.