I'd say, if you're aiming for realism, that she probably shouldn't be moving the knives back and forth as much as she does in the current sprite, since the amount of movement kind of looks like what I'd expect for a crawling animation rather than an idle pose.
I've just done some quick searches, and while I haven't spotted any dual knife videos, there's one of an exhibition match which belongs to some History Channel program:
https://www.youtube.com/watch?v=rkHwe0anWnk
From what I can see, it looks like knife fights aren't just about the weapon, but also about diverting your opponents' attacks with your free hand. Given this video, it looks like a reverse grip is better for defense, while a forward grip's strength lies in offense, so I'd say that perhaps your character could use a kife in each position? I guess the dominant hand would have to take the forward grip and be used for stabs and long-range slashes, while the reverse grip could do short-range follow-up slashes for combo attacks as well as counters (can you even parry with a knife?).
Alternatively, you could have her keep the non-dominant knife holstered, perhaps on her waist rather than her leg to allow for faster retrieval, which'd also allow her to better counter enemy attacks with her now free hand (if that's something you want to do in your game, that is).
