I don't think this is a very good one, and I'm not convinced that the GMAT would consider D definitely correct and C definitively incorrect. "Showing" in D is a bit odd, since the preceding clause just says that she is notable. I get the meaning, but it's a bit odd to say that she is "showing" something simply by
being notable, rather than by, say, winning races. Meanwhile, as others pointed out, C uses "which" as an essential modifier. The GMAT generally avoids this. (Adding a comma wouldn't help; in fact, it would designate this as a non-essential modifier, and it's definitely not.)
We also don't need to worry about "changing the meaning." That's not a thing in general. We only worry about missing words if one of the choices leaves out a concept that the others are clearly trying to convey, and that's not happening here. Nor do we want to cut C because it is "awkward and wordy." That doesn't mean much either. If C fixed a clear problem in the other choices, it might use some extra verbiage to do that.
So, short version: there's a fairly official reason to cut C. It uses "which" to create an essential (aka "restrictive") modifier, and the GMAT doesn't like that. But otherwise C is fine. Since D is a little sketchy, I don't fully endorse this question.