Tsunade wins.
Remember she has a pathway disturbance jutsu to **** up the nervous system. One touch and Mei will move her toe when trying to move her arm, lol. Tsunade can aswell manipulate the ground, there isnt much balance for Mei when she inside an earthquake is it? Tsunade has also proven to make a earthen shield by punching a piece of the ground.
Tsunade is also an excellent dodger, she avoid attacks pretty good considering shes not suppossed to get hit, so she doesnt use chakra on herself, but her teammates.
I think Tsunade is to fast for Mei.