You will her to notice all further changes, but for her to find them curious and exciting instead of scary or freaky, you will her to fetishize her changes, slowly. You will her to be unable to cum at all until you are finished changing her or until you wish otherwise. Easy, right? You decide to give it a shot.
You grip the wand and wish for her nipples to disappear.
You watch her nipples intently as they bounce around while she masturbates. You don't see it right away, but then you notice it. Yeah, they're definitely shrinking.
"Whoa!" she says, noticing the change. "That's interesting."
She continues pleasuring herself as she toys with one breast, feeling at her nipple while it shrinks into nothing but a small nub on the tip of her breast, then nothing at all. You raise an eyebrow and take note that her masturbation has intensified.
"Aww, it's gone!" she giggles. You smirk, this was almost too easy!
You think you've proven that your spell has worked. You wish for her nipples to return - at double size and double their sensitivity. You smirk as a flesh color bump forms on the tip of her bare breast. It darkens to pink as the skin around it starts to rise, forming small bumps that spread out around the swelling nub's diameter. "OOOoooooh!" she cries as she flicks at it with her hands, now rocking more aggressively in her place on the bed.
The nubs continues to swell, darkening still to a dark pink, and pushing out into her teasing fingers. Her nipples were large before, but as the spell continues, they push out and end up at nearly the size of your pinky finger. Her masturbation increases to a furious mix of mad thrusting and rocking her legs, extending and releasing as her pleasure just builds and builds.
"Fuck me!" she moans.
You smile as you will your next change to take hold. Her breasts begin to fill out slowly before your eyes. They were gorgeous G cups before, laying upon her chest like globes, but now they begin to surge out even more. Pushing down past H and then HH, and then further as her breasts travel down her body. One hand molested her nipple as her breast grew beneath it grew. She looked down wide eyed, finally taking notice of the colossal swelling orbs upon her chest. Her eyes bulged. Her body quaked with pleasure as They grew to LL cups. Then M. Then MM. They now hung down past her belly and proceed to push down closer and closer to her heart shaped tattoo.
She now has breasts that would make pornstars' jaws drop. Further down they grow as she hugs them closer as writhes uncontrollably. Her left hard worked the vibrator furiously into her clit. Her right hand kneaded, teased, squished her nipples in the most creative ways she could imagine.
Her breasts were now enormous. They hung down to her pussy easily, and were actually beginning to impede with her self-pleasure. She didn't to want to stop, nor did you want it to, but maybe you could play with her in other ways? You knew this could go on forever if you let it.
"I don't know," you think. "Maybe we can think of something else."