The stone doesn't work for Karyn

Karyn was unimpressed. "Can you explain to me why men are so shallow? Everyone knows that McMillan is a total bitch and yet, because she has blond hair and big tits, every guy in the school spends half his life dribbling down her cleavage." "Not every guy," I noted, although I had to admit that Sarah wasn't bad to look at, even though I'd never associate myself with someone with such a untrustworthy character. "Okay, most guys. There's only one of her; why can't she just pick one and let the rest of us have a go?" She sighed. I grinned. "Got your eye on anyone in particular?" I asked, trying to sound nonchalant. She scowled at me. "No. Just a general feeling. God, I wish I had long blond hair and big boobs and maybe then I'd get some of the attention." I think it dawned on us both at the same time what she had said and we just looked at each other, a look of slight shock on our faces, but then... nothing happened. “Huh,” Karyn muttered. “You really need to be careful what you say while holding that thing,” I warned, watching her warily. I was already trying to figure out why her wish hadn’t triggered. She’d held the stone. She’d said the words. By all logic, she should’ve been halfway to Barbie-town by now. “Yeah, yeah, I remember—wishes can’t be reversed, blah blah,” she said, flipping the stone in her hand. Then her eyes gleamed with mischief. “I wish Jon’s hair was blue.” “Hey!” I clutched my head instinctively like it would ward off the magic. “Relax, drama queen. Still brown, same as it always was” she said, as she tossed the stone back to me. I caught it and frowned. “Is it broken? I wish I had an ice cream cone in my left hand.” The familiar pull on my vision hit me, and I quickly glanced away. A second later, a perfectly formed vanilla cone appeared in my hand. I yelped and dropped it onto the grass. “Yeah..." Karyn said, pondering, suddenly with a sense of realization "That makes sense.” “Makes sense how exactly?” She crossed her arms and gave a thoughtful nod. "I'm far from an expert, but as I understand it some magical artifacts can only be weilded by humans. It's kind of like... I don't know... trying to pour jet feul into a tank that’s already full. It just won't work on me" I stared at her. “Wait. Karyn… Are you saying you’re not human?” She gave a sheepish little shrug, then grinned. “Well…”