Well, she is the proto-Pinkie and by this point nobody would recognize her if she didn't look like Pinkie. By now, coincidentally looking like she could be Pinkie's twin is part of almost everyone's headcanon.
"I wanted to visit the ground world, but I was too scared to go down there. But suddenly, an idea. I attached to myself a couple balloons and floated gently to down to the ground. And that's how I got my cutie mark."