Katie and her fraternal twin brother, Theodore, were born evil. Little else can explain the twisted relationship that they developed so early in their childhood or their utter lack of conscience, despite the perfectly normal childhood they shared. The incestuous pair arranged an accident for their parents when they were barely thirteen and then manipulated their foster parents until, in the midst of the mental breakdown of their foster mother, they struck out on their own. Both were just past their majority when they were arrested in connection with the murder of a man who had allegedly tried to rape Katie (in truth, she was seducing him in order to rob him and her brother, in a fit of temper, struck the deadly blow) and that is when Martin LaSalle involved himself, using his connections to get the charges dismissed and the twins released into his custody.
The reason for his interest was the shared mystical talent that the two shared. Not only did they exhibit strong indications of telepathy between them, but Katie was an actual spiritual medium, a gift which she occasionally used for money and which is what drew LaSalle's initial attention. Testing them, he discovered that both had far more talent than he'd hoped and he Embraced them both so that they might become apprentices. Unbeknownst to him, however, the two inadvertantly Blood Bonded each other before he was able to and so have no particular loyalty to their sire, other than the fact that he is currently useful as a mentor and money source.
Katie, always the quiet and manipulative one, has focused her studies on the arts of corruption and spirit manipulation and uses them both to blackmail people into getting what she wants. The former path she uses to force people into acts that she can use against them, and the latter she uses to get intelligence. All this information is turned over to her brother, and selected bits are fed to Martin to keep him sated. She doesn't just extort from her sire's enemies, either. She has managed to get all of the other apprentices Martin has had under her thumb as well and has dirt on several members of the Camarilla in Baton Rouge and even a few Sabbat members (she is aware of the revenant spies in Baton Rouge and Lake Charles, for example, but has yet to share this with Martin).
Her studies have progressed to the point that Martin is ceasing to be useful as a mentor and she is beginning to look for ways to work her way further up the later or perhaps transfer to a larger, more prestigious chantry. To do this, she is perfectly willing to discredit her sire or compromise him in any way necessary. Her brother is aware of her general plan, but not the specifics, but supports it fully, nonetheless.
Katie is a psychopath and tends to play the part of a quiet, retiring, fragile woman and play upon the protective instincts of any men in her life (including her brother's). She is constantly looking for ways to amuse herself, as she suffers from the tendency towards boredom that most primary psychopaths do, and much of her blackmail and the hideous "experiments" she encourages her brother to partake in are for this purpose. At present, toying with the youngest apprentice is sufficing to keep her entertained.
Katie loved her brother as a child, but the artificial emotions of the Blood Bond have made the link between them all the stronger and even more of a contrast to their otherwise emotionally dead mental landscape. Because of this, she is fiercely protective of him and will do anything to make sure that he isn't harmed.
Her feelings towards her mentor and the other Tremere are less intense. As previously noted, she only cares for Martin as long as he is useful (which isn't much, lately) and sees others apprentices and sources of amusement more than anything else. She does have some small loyalty to the Tremere in general, however, due to the ritual of her Embrace, and won't usually do anything to harm the interests of the clan.
She has little respect for the Baton Rouge Camarilla, seeing them as generally weak and easily manipulated, but has a growing respect for the Lasombra of New Orleans, whom she sees as worthy adversaries. Her involvement in Baton Rouge's plans are mostly grounded in this desire to test her skills against skilled opponents rather than any sort of sect loyalty or idealism.
She has acquired quite a bit of clout in Lake Charles and Baton Rouge through her extensive use of blackmail, though she rarely uses it, except when convinced to take part in the chess game with Delacroix and his pack.