"Before I make my wish, I have a question: if I wished someone turned into a werewolf and they bit another person while they were transformed, would they cause that person to become a werewolf?"
"Yes."
"What if the werewolf bit me? Would I become a werewolf, even though I have recieved the effects of a wish someone made with you?"
"Yes. Being changed by the bite of a werewolf is an effect from the werewolf itself."
"Then I know my wish but it is a little complicated. I will begin to make my wish then let you know when I'm finished making it, okay? No cutting me off because I pause for breath or anything, right?"
"Of course."
"Okay, here is my wish. I wish that Jim - the guy who is my current boyfriend who wished me to become a mermaid - would transform temporarily into a merman and not know why until I tell him. This change will begin the next time he takes a shower but will not be complete until we are alone together. He cannot change back to human until he has sex with me - and he will be able to do so. As a merman he will have a power: anyone he has sex with while in mer form gains the ability to switch at will between human and a mer forms and breath both in the water or out of it. When they switch into mer form they have the same gender as they do in human form. Anyone who gains this ability also gains the ability to pass it on when they have sex in their mer form."
"A complex wish indeed" says the genie with a bemused grin. "Is that all?"
"Yes, that completes my wish. If I worded it right, Jim will know what it's like to be changed into a mer without warning and having someone else control when you change back. But he'll also cause me to gain the ability to change at will instead of every time I get when in a swimsuit because it's like the werewolf bite scenario we discussed earlier. And in case we like going mer-on-mer, I pass the ability on to him as well - but since the change is at will he can chose to remain in human if we don't like it. As a little girl I thought about being a mermaid, but I've never really though about mermen before. So did I close all the loopholes, genie?"
The genie grins at you. "You will find out soon enough." He snaps his fingers then vanishes along with the lamp, leaving Lydia alone in the basement still wearing only a pair of jeans.