Her brother (who wasn't actually her brother) had been a slave/guard. Both tieflings though, and they bonded. He tried to look out for her, which got harder once she started manifesting sorcerous powers.
Then they both got punished, he got lobotomized so that he couldn't speak or understand words, and they escaped, fleeing south into the River Kingdoms.
She was a habitual liar, a little vain, fond of her power and loyal to her 'brother'. She also had balls, a pair of big brass ones, and while everyone was still freaking out over a dragon having flown in and declared itself in charge of a city, she walked up to the dragon and between flattery, bluff, and bravado managed to get a job as the dragon's right-claw minion. Talk about a promotion, right?
As it turned out, one of the reasons the dragon liked her was because making this random foreign ex-slave her prime magistrate really pissed off all the established powers in the city- but who's going to argue with a dragon? Or a sorceress with a loyal, mute, fairly competent bodyguard? And the tiefling, well, she liked upsetting nobles too- a heck of a chip on her shoulder. "Look down on me for having been a slave, will you...?"
She tried to use her position both to heal her brother and to throw some work the PC's way, who had rescued her at one point. As much returning a favor owed as showing of her new position and power to her friends.
I enjoyed her as an NPC.