Trying

"Just calm down" John thought to Sarah, "Wish for another shrink ray and I'l shrink myself down to a more reasonable size then enlarge you." He was surprised to hear that he now thought with Sarah's voice as well.
"No way, who knows how much smaller I'll end up if you screw this up again. Impulsive wishing got us in this mess, we need to think this through before I make another wish" Sarah said.
"Fair enough", John replied, even though he really wanted to get to a normal size soon, even three feet was better than this. He was starting to feel cramped in the room at this size and his enormous breasts were being pushed up against his knees in a very uncomfortable way.
"Which shoulder are you on anyway? I can't feel you" John wondered.
"I'm not surprised, I could build a house up here. I doubt you'd be able to feel me. Tell me, can you feel this?"
John concentrated and thought he maybe felt a small scratching feeling on his left shoulder but it passed quickly.
"Maybe, are you on my left shoulder? I felt a small pinch"
Sarah laughed as she said, "Yup, that was me. I bit you. Anyway, enough of this nonsense, I think I have a way to get us both normal sized. Here I go."
John heard nothing but soon the room was getting less cramped. With a flash he was finally Sarah's normal height of 5'5, still shorter than he was used to but better than before. He didn't see Sarah anywhere though and wondered where she was. He called out to her but there was no answer. Remembering the telepathic link they now had he called out to her mentally.
"Turn around", she said to him.
With a very bad feeling he slowly turned around. There was no one there.
"I can't see you" he told her, checking under the bed, the dresser, and anywhere else a shrunken woman could be.
"Look outside", she suggested.
He approached the window, not knowing what to expect. When he got there he saw Sarah's now giant face looking out at him.
"Wha... How did you get so big?" John stammered in his head.
He could feel he laughter vibrating the room as she said, "Oh, I'm not big, you're small. Come on out on the balcony and see"
John didn't move and Sarah banged on the wall of the dollhouse, knocking him off his feet. "COME OUT!" She demanded.
He nervously opened the window and stepped out onto the balcony and saw he was in a dollhouse on a table in Sarah's room. Sarah was sitting front of him looking down on him with a look of triumph. The stone was nowhere to be seen but he knew it must be nearby.
Sarah saw him looking around and laughed as she said, "Go ahead. Try the stone. It won't work for you anymore." She placed the stone, now a boulder to John in front of him and he ran over to it, embraced it and said, "I wish I was safe at home with the stone". Nothing happened. He tried again a few more times, but no luck. He tried everything he could think of, wording it differently, using his name, even French, but nothing worked. All the while, he could hear Sarah laughing high above him. After a while, she took the rock away and said, "Ok fun's over. Now it's time for some show and tell." She pulled out a makeup mirror and put it down in front of John.
"Yeah, I know. I'm your twin. That's hardly a newsflash" John pouted.
"Wow, you're dense. I can't belive you can't feel it. Here let me help you" Sarah said as she grabbed him in her hand turned him around. With her other hand she carefully turned his head so he was looking in the mirror. On his back, he now had a pair of beautiful, translucent wings. Just like a..
"Fairy!" Sarah exclaimed, "When I was so small you couldn't hear me I was making a bunch of wishes. You didn't even notice but we were both in the dollhouse almost immediately. From there I just wished to know how to do something and the stone told me. And guess what the best thing it told me was? Magical creatures, such as fairies, are unable to use the wishing stone. Enjoy your new life, Tinkerbell." She laughed and laughed as John fell to his knees and started to sob, pleading for Sarah to change him back.