While I see your point, I think there is at least a solid ground to be made here to accept that Law's damaging Meme's internal organs made it easier for Kidd to break her bones via blunt force, which ordinarily wouldn't have been possible. After all, any damage to internal organs will always directly affect the stability of your health, especially in a high-risk situation like this fight.
Then again, I see this fight as a combo of Law's internal damages + Kidd's external damages, anyway, so if you think differently, that is also understandable.