After attempting to leave her home she tries to battle you to keep you with her and tries to kill you but can't bring herself to do it so she gives up and lets you defeat her. But out of nowhere you notice that you have a new option, instead of "Fight" "Act" "Item" And "Mercy", you know have the "Hypnotize" option, and you decide to try it out

Toriel: W-what are you doing my child?- almost immediately after she says that she completely gets hypnotized and is now under your control

Toriel: I am yours my child..