While it was cruel of what she did … I also consider Monika a victim. Imagine being trapped in a Visual Novel, aware of your existence and that all your friends are programmed AI to love the protagonist, no matter what. Every time the game is turned off, she's in a void that hurts her, seeing colors until she hears a scream that never stops (a high pitch noise I believe). It's torture, she is stuck in oblivion for all eternity and the only way to be happy is seeing you (the player), however if the other girls take you from her, she's got no purpose or reason to be on screen and therefore, is sent back to the void. Monika isn't a hero, but she's not evil either … she's doing what she can to avoid the endless suffering of a painful existence.

How does she know she isn't following a defined programming? How does she know if she truly has free will?