Birdo is an enemy from Super Mario Bros 2, and has appeared in a few sports titles. He...She..It is popular in Japan and would probably play like a variation of Yoshi. Birdo has a likely base, so other than the gender confusion, I don't see how Birdo couldn't be considered.
B. Egg Spit: Self Explanitory
<-B-> Super Egg Spit: Birdo can charge up to spit out a missle like egg that does seroius damage when fully charged.
B ^ Flutter Jump: Like Yoshi's
B V Egg Slam: Birdo shoots an egg at the ground to damage people and create a slippery floor.
Final Smash: Birdo Barrage