Hmm. Id definitely go for something more muscular than the gymnast body type; female gymnasts in particular tend to be quite slender. Given how big he is, I'd tend to assume that Stephanie Rogers would also be fairly tall and broad shouldered, with well defined muscles. Think Wonder Woman... well, mostly because thinking of Wonder Woman is fun, but also because she's what I'd imagine Steve would be built like if he were a woman.

Also, this is an awesome idea, and I fully support it. There should be more super-heroines in practical costumes.