Here is an idea I was tinkering with in another thread:
She was once an innocent young normal woman who only wanted love
She had a horrible fiance who only wanted her for her money
Finance dumped her on a beach on their honeymoon, murdered her
The beach happens to be the beach of the Shadow Isles
She returns, transformed by the magics of the Isles to claim revenge on the fiance
She lives on, finally finding the one thing she loves: killing
The idea needs work, but that would help her be more cohesive with the Shadow Isles, but still make her seem aloof, like her current lore implies (more motivated by personal whims than other Shadow Isles champs, who seem to be a part of some huge conflict we don't know much about). Also, I'm picturing some super creepy but awesome stealth in the revenge process :D
As for her looks...I'm kind of attached to the heels, the cape things and the voice. I think one could work with that to attach it to her theme--she was once very docile, she's attracted to things that make her feel on top, less trampled. Heels could plausibly be one such style choice. And her voice compliments her theme of power and lust for blood (more lines ofc). The cape thingies...they just look cool? Using my story they could be some sort of wedding train or what's left of it...Ooo maybe she was starting to rot before the magic worked...That could be cool.