"You know…" Said Kelly, with shyness. "… I want to stay that way, I think. Can you let me make some wish, to make my new life comfortable?"
I then extended my arm, thinking she was going to take my ring. Instead she just grabbed my hand with hers, making sure to touch it with both.
She then started wishing, and each of her wish was granted, altering reality even more. But since both of us were in contact with the ring, we still remember what reality used to be before these wishes of her.
First, she wished that peoples turning into centaur wasn't unheard of, just an extremely rare occurrence. Said transformation isn't hereditary in any way, but thanks to modern medicine, we can know within a week if a newborn child will later become a centaur. Kelly then wished to be a late bloomer, and the changes to usually happen during puberty.
Realizing her new anatomy will bring hell on her human back, and remembering that horses usually sleep standing, she wished for a centaur's anatomy to prevent that. First, long hairs grown on her spine, from the base of her human back to the base of her head, connecting with her human hairs. Then something shaped like the back of a horse neck in it's global form and size grew out of the same area.
Not wanting to force centaurs to live in a world made only for 'normal' humans, she wished that, since humanity is, everything was always made, if possible, to be usable comfortably by both humans an centaurs. When it was impossible to make something for both, and it wasn't something centaurs will not use then, and only then, it existed in two different version. One for humans and one for centaurs.
The impact of that last wish was even greater than any of us would have imagined. It changed how towns and cities were build! Since they were build with centaurs in mind, they were now having a big park in their heart, bordered by the surprising blending of the now indistinguishable financial and residential districts. Most important locations got more than than one park, making them look more like a grape of towns than a single city.
"The boss must have heard of my change now." Kelly said "I doubt we have much time, but I have one more wish…"