Suggested by iKnowledge Thundra is a very strong fighter and can hold her own with most in terms of physical strength. That said, she will definitely be on the back foot against Tsunade here who also has great healing abilities and speed. She should be able to crush Thundra in hand to hand and handle any attacks that she dishes out in the meantime. The gap between them is fairly sizable and the Hokage is not losing here. Tsunade wins.