There's no way that she'd make it into Smash 4 anyways. You guys are lucky that she's an costume of Peach's. That's the best you're going to get.

I say that because there are simply many more important characters.

These are the main ones, and have no doubt whatsoever that they will be in before her:
Toad
Bowser Jr.

There are even more than that, and I hate to tell you, but it's very unlikely that there will be an addition of more than two Mario characters in the next game.