Can't undo wishes

I looked around in confusion...nothing had changed. "What the?" I asked in confusion "what's going on?" "Wishes can't be undone remember?" replied a voice. I looked up to see Zoe leaning on my doorframe. "Huh?" I asked as she entered, closing the door behind her. She smiled and sat on my bed. "The rules of the stone - you can't unwish a wish," she grinned. "How?" I asked confused, not knowing what she was implying or how she knew about the stone. "Because I already wished it," she grinned, "I used to be the eldest - your brother Zachary - and you were my gothy little sister Jen. I made the wish you did to change lives and..." "You became Zoe the Goth and I became Jon the big brother," I finished, dumbfounded.