Ms. Grunkle doesn't try to turn you into a monster at all... until the very end of the game, and when you're going through her house, she throws you into the labyrinth rather than turn you into a monster because she's toying with you. Actually that makes a bit of sense - she's toying with you throughout the entire game, and wants you to think you've won before pulling out her trump card. Good thing she dropped her wand, otherwise she would've won.