I've still not decided what is causing her to have random mutations over an extended period of time like this. Maybe a disease of some sort. Or a heavy overdose on transformation potions. Or maybe it's just a thing that happens naturally to some people, like puberty on steroids. Or maybe a fourth option... Meh, screw it, I'll just leave it to the viewer's interpretation.
By the way, here's something I've been thinking about: how many cleavages do multi-breasted people like her have? Take this girl for example; the easy answer would be 3: one cleavage for every pair of boobs. But surely, a cleavage is just the area between two boobs that are next to each other, right? So, by that count, she has, like, 7 cleavages. Or 11, if diagonal cleavages are a thing. Yeah, I know, deep and insightful stuff, innit?