Change the personality of another
Prewett gift is very powerful, as she is able to create vampires who manifest a special gift. She can change her targets personality altogether, giving them a different mood or view of something. Prewett has only ever used it (as far as we know) on her coven mates while they were humans. As vampires, her covens are still a little unsteady and can't stay still like vampires usualy can, this could be an affect of her ability or an affect of being changed while they were effected by her gift
Prewett has used her gift countless times over the centuries, her coven mates are an example of her power, when they were all human, she had twisted their personalities so forcefully that they manifested special talents after they were changed into vampires
Prewett can only alter the personality of one person at a time, and like most special powers, it seems weaker on humans, Prewett had to concentrate on her coven mates when they were still human.