I just found an older story at the BE Story Club, called "Pretty Angry". The story is about a girl named Shelly, and Shelly has an attitude problem. A white witch decides to teach Shelly a lesson, so whenever Shelly is mean to anyone, her breasts grow. The illustrations are by PortalComic and they're very good. The author is somebody named MysteryIncCB.
The illustration above shows Shelly after her first growth phase. (She gets a lot bigger.)