Sooooo Basically you are doing a genocide run. You killed Myno a long time ago, but through her determination, she rose back from her dust and came back to stop you. Seeing her dead brothers, Papyrus and Sans, She became more mad. Seeing what you have done to them, makes her have no love in humans anymore, now she has LOVE for humans, all because of you. Right before you reset, she enters a fight with you and stops you. She knows even if you reset she will not forgive you.
Credit ttttoooooo pocockikapusta Sprite : Internet