I think she's like Misato, in that while she does seem like she could just be fanservice girl, the way it's portrayed in the anime/manga puts her firmly in control.

And yes, I bought the first volume on impulse, and while Black Cat doesn't do much for me, Sven, Rinslet, and "Ivy" are awesome.

I love when Sven's all like, "i'm going after her" in the end of volume one.