Obviously

You were sitting across the room from her, with your back to a wall, so you could easily open up facebook or something on your phone to browse photos, and you opened up her profile, to see what recent pictures there were. The most recent one was actually uploaded today, she was sitting on the wall outside with a friend with a grin which was unusual to her, at least it was before you changed her resting face. She was leaning forwards slightly, and your eyes were drawn to her boobs, obviously.

Because she was leaning forwards, they looked slightly larger, and because at the same time she had her arm around her friend, her shirt was pulled taught, which made them look even more perfect. You looked up from the phone, and decided you wanted to see what she looked like with D cup boobs.

You focused again and watched as she took a sudden deep breath of air, sitting up from her slouched position, straightening her back, and pushing her breasts out slightly. She didn’t realise anything, as she just assumed this was how she normally sat. You didn’t see her return to her normal posture, or push her boobs back in, because they started growing. In the previous change you also changed all her clothing to match, so her white shirt and bra was growing with her new chest, but, it seems that in this reality, she was a bit more adventurous. Her shirt was now very clearly a tight white top, but she still wore the black skirt and cardigan. Scanning her mind, you discovered she was still rather shy, and easily embarrassed. You make a quick addition to her personality and mind, in that she enjoys people looking at her boobs. After this addition was made, you looked at her posture again, and she was sitting with an even straighter back, and her boobs were sticking out even further.