Talk:Undyne/@comment-26967580-20160810200539/@comment-27701762-20160810204528

You are unable to befriend her on that run, meaning you cannot complete a True Pacifist playthrough unless you Reset.

Undyne returns to her house, and Papyrus is waiting outside (assuming you've befriended him already). He notes that she got heat stroke as is incredibly sick, and thus unable to hang out (not to mention that she is still muttering about destroying you).