You forgot that she was out of chakra when she took care of naruto. Then how could she finish the seal if she was empty ? Tsunade nearly never fought for years to dev it, so it's logic, here something is wrong.
So the point is : is she like sasuke in mid shipuuden? She have magic supplies of chakra that appears with no logical reasons for the plot sake ?
Right logic, wrong time line.
THIS is how it went:
1. She spent 9000 chapters fighting Obito & Madara & Juubi without activating the seal (though I refuse to accept that she COULDN'T activate it an hour earlier).
2. She finally activated the seal the moment she saw Sasuke (let's skip the idiocy of her timing for now).
3. She kept using it for SMASHING, TANKING and HEALING, until she openly claimed to be drained of chakra as of CPR (OK, fine).
4. Then, a short time later, she suddenly AGAIN has enough CHAKRA for a few DIMENSION-JUMPS with Failbito (er, WHAT???).
Sorry, but IF she was able to regenerate IMMENSE amounts of chakra in such a SHORT time - WHAT KEPT HOLDING HER FROM ACTIVATING THE SEAL THE ENTIRE DAY EARLIER???
THIS is what I call an
ASSPULL.