Here's the dialogue from when she knocks away (or rather, throws a spear at) the Flowey-role (who is a candy bowl): NGAHHH!!! Get away from them, you hollow piece of wood! Oh, sorry to scare ya! I'm UNDYNE, the guardian of the Ruins! Sorry about Asgore...he tends to cause chaos around here occasionally. I should probably show you around the Ruins before I do anything else. Follow me!
Here's the dialogue from before her fight: You wanna leave? Punk, if you head out there, you're gonna d!e... Just like...the OTHERS... ... Nothing, huh? You really are brave. But it's time to put that to the test. Show me. Show me how strong you can really be!
