What Should He Do?

She becomes a reality bender.

John thinks of a way to change her, and once you find the perfect way to do it. "Excuse me, I have to go to the bathroom", as you leave the room.

John enters the bathroom as he says "My aunt has always been stubborn, taking anything for a literal challenge, starting now, reality will bend to her will to complete that challenge, no matter what it is, she will never pick up that she can bend reality, and just think she's extremely skilled." you wait a few seconds, you make another wish just to see her now "Due to living troubles, I have to live at my aunt's house, I sleep in my own room and have all my belongings in it", and make it seem like you went to the bathroom, before you came back.

"Hey auntie" you say, "I bet you can't lift the couch you're sitting on with one hand!" Your aunt looks at you with a grin "Is that a challenge?" she stood up, and picked it up with, you guessed it, a single hand. You were glad and worried it worked, but you wanted to see where it would be taken.