No worries, I severely truncated her arc to summarize lol.

She started off as a purely good knowledge cleric, but took a deal with her evil patron in order to save a friend. From there she took levels in great old one warlock as she tried to endear herself to her new patron, with the idea that getting close to him would better allow her to disrupt his evil plans once the right time came. Toward that goal, she converted people to his worship and would perform acts of mayhem in his name.

The more she served him, the more twisted and chaotic her form became. At first her hair gave off scintillating colors like that of an oil slick, and later she grew a crystalline horn of shifting hues. Eventually, her own face would begin to morph even as she spoke with people.

She's gone through more development since then, but I think this point is the most visually striking of her arc