The hail mary.

Jon pondered the situation, and then spoke again. "I wish Karyn could so completely transform into a human being that she needs to breathe, eat, drink, and can even reproduce. I wish all of her children will be normal humans, subject to further wishes. In fact, I wish her teeth, permanently, and one other thing about her remains couchlike. On very close inspection by a dentist these are normal human teeth shaped pegs made out of button brass, and are covered with dental enamel, and that this and one other unspecified couch-like aspect about her which she can instinctively change to keep her couchness concealed is all the couchness that will be required to satisfy the wish that made her into a couch." Karyn waited in expectation.