A female cosplayer of Triple D? Or is she one of those "gijinkas" that I've read folks namedropping from time to time? Either way, she looks like she can hustle, which will certainly help with getting in on MegaOrangeYoshi's Buster zoning, as well as being able to chase after him if he decides to run around (including in the air, via Flutter Jumps, Super Jumps, & air dashing). She also looks like she doesn't have as much defense as the penguin, so she can't tank as many hits as him. However, she could be like Neva or Cielo or Chartette from Wonderful World (PC only), who can deal truckloads of damage per hit (especially Chartette, whose Forward HS, despite its incredibly long startup, can deal 50% HP worth of damage in 1 hit for no meter at all. I'm serious.), so she wouldn't have to land as many hits as MOY would have to.
'Course, being a Yoshi, he's got the speedy upclose melee abilities to compete with her at close range, should she get in on him somehow, which puts him above plain ol' MM in that sense. Also fitting of a Yoshi, in terms of melee range, her hammer will disjointly outrange him. He's also got overall high mobility, including numerous other options I didn't mention yet (KOF styled rolls, Slides, cancellable backdash).
I'm really not sure who'd win this in a realistic sense. I suppose whoever gets the momentum and keeps it will likely win.