I can recount my own experiences with her... I never really knew her until a game she threw that one game with Gambler. That's when things started to go badly with Mirror.
Like others probably described her first personality... she didn't understand a lot of what the blanks showed her. She was like a child who was learning about principles and morals, emotions and social standards.
That game threw a huge wrench into her development, from what I can tell. In this cycle of blanks.