What are you talking about she isn't strong?
Let me remind you that Tsunade is the strongest ninja EVER, in terms of brute strength.
The greatest medical-nin who ever existed, she was also the creator of the Creation Rebirth. It instantly regenerate's one's body to it's healthy state when he or she is injured, organ's are no exception. How OP is that?
Infact, if it weren't for those Four dead weight Kage's, Tsunade could've possibly beaten Madara.
Body Pathway Derangement solo's baddy Madara. Heck, even a Chakra Scalpel would solo him.
Without edo and those good-for- nothing Kage's Tsunade would be spamming Creaton Rebirth until Madara just let's her finish him off.