It's sad how everyone is saying Tsunade is not a fighter, she's a healer.
Yes, she is a healer, but she is also a combat type ninja. Look in the databook and look at her 5, compared to Kakashi's 4.5 in taijutsu. Not a big difference, but a difference nonetheless.
Sure, he has her on speed, but not stamina, meaning if she picks up on his attack pattern, which she is most likely to do given her years of experience over his, then she is likely to outlast. Let's not also stray from the fact that Orochimaru stabbed her with his sword, and she was still able to move around and kick him away from her. So odds are that he can probably stick her with the Rakiri, but if he misses her heart or head, then he's pretty much doomed because I don't see how he can pull his arm out of her (after he's stabbed her with Rakiri of course) faster than she can knock off his head with one of her punches.
Even Kamui won't help, because it really only helps in a linear direction meaning if she does some zig-zag action, it will taking him some time to try to hit her with that.
Also notice in this scenario I didn't even say that Tsunade needed Sozo Saisei (Creation Rebirth) activated.
I'm going with Tsunade on this one.