With the caveat that we're putting aside that whole "lol cape-comic women have the same body" which is fair, really. Does a Marvel character like that exist?

In-Universe acknowledgment of her "assets" should exist, and the character would have to fit in one of these tiers:
Tier 1: Breasts that rival Power Girl's in size and notoriety.
Tier 2: Ass/Legs/Hips that rival Power Girl's breasts in size and notoriety.

I was going to throw in that the Marvel character should be as well known as Power Girl, but that's just asking too much at this point.