You decide that it is time to take things to the next level with the wand. Now you're not set on physically changing her body, although your hesitation is due more to not knowing what to change than being afraid of the consequences. One thing you did desire to change was her attire. As said before, Jessica had the tendency to wear tank-tops and short shorts around the house for comfort. Today though, she had decided to wear a slightly over-sized white t-shirt. It hid her chest well and was rather unflattering to her curves, which was probably the furthest thing from her mind, being casual wear. Thanks to the wand though, the choice was up to you and since you wanted her wearing that tank top, she was going to be wearing that tank top.
After giving her large tits one last squeeze, you remove your hands from her shirt and grab the wand. You aim the wand at her t-shirt and will that "Jessica's t-shirt will transform into her usual tank-top". The change isn't instant; In fact, the delay almost makes you believe that the wand wasn't able to change nonliving things like clothes. Almost, that is, until you notice small holes beginning to form around her t-shirt. One above her bust, two on the arms, and one above her spine, to be more precise. These holes slowly grow in size, revealing more flesh as the disintegrate the fabric of the t-shirt. Eventually her sleeves are completely gone, exposing her shoulders and armpit areas like a tank top would. At the same moment, the area above her bust evaporates into a U shape, revealing the bountiful cleavage you are used to seeing on Jessica. Her back also finishes at this time, exposing a fair amount of her shoulder blades. Overall, the only part of her upper shirt that hasn't disintegrated are the spaghetti-like straps now holding the piece together. The final change was the fabric itself, transforming from the slightly rougher t-shirt material to whatever her tank top had been made out of.
Still in your position behind Jessica, your position gives you a great shot down her tank top. Without any bra to cling to her flesh, there exists a small gap between them and the top itself. Her nipples are thus exposed, giving you your first glimpse of them. She'd been careful to not nip-slip in the past, so this was a big deal for you to see. And yet, you had an idea. Sure, this was hot, but why not make it better? The wand could shrink the top and fit so snugly that it'd act like a corset of sorts, improving her cleavage and overall appearing sexier.
Seeing Jessica as nothing more than a guinea pig for the wand, you make the change without a second thought. Unlike the previous change, this one happens almost instantly. The loosest part of the tank-top, her bust line, begins to contract inwards; the gap between breast and cloth is soon closed. It doesn't end there, however, as it continues its journey inwards. In a normal situation, the fabric would have ripped first in its struggle against her large bosom. Thanks to the magic though, her bust is instead pushed upwards, giving it support and deepening her cleavage quite a bit. You smile to yourself as you examine what can best be described as an overflowing tank-top.
Jessica, thanks to your first spell, doesn't really notice this either aside from some attempts to adjust the uncomfortable tank-top. It seems that this counted as you interacting with her and thus spared her from noticing. Saves you the trouble of dealing with her freak out, you think to yourself.
You got what you wanted and can't be happier. What's next?