30 years. That's how long it's been since Sarah was turned and in all that time, she never learned. She was cruel then and just as terrrible now. When she'd been turned, a part of her snapped. Sarah has no humanity left. No compassion. Or at least, that's what most people believe.
The only person she's ever cared about after all this time is her neice. It's not so much a maternal instinct or human nature, but an odd way of looking at their relationship. Paige keeps the vampire feeling as if she's still alive. As if her life matters. In her eyes, Sarah can do no wrong and for a vampire who's lost all human nature, it's nice to think someone believes you're still decent.
Growing up in the time period she did, Sarah was expected to play nice and act as a proper lady but that never stopped her from going against her parents' wishes. It was her sister who followed along and it was her sister that ended up dead. See where being nice gets you?
The Holland family is renowned for their brilliant minds. Every Holland ever created was intelligent and to be married into the family meant you had to have the brainpower. They all followed the same path, using their smarts for the greater good. Sarah preferred to get rich and live a little.
Shortly after she was turned into a vampire, she went on a crime spree that landed her in the grasps of petty thugs. Eventually, her cruel nature earned her a place in their ranks and she worked her way up their social ladder. Now, she spends most of her time not just pulling jobs but creating chaos.