I'd go with sleep deprivation. Fairly easy to cause (especially if the target lives in flats/ terraced housing- just buy the neighbour's twelve year old kid a drum set) and can really screw up someone's life and personality.
Also, if you really want to screw up her life, don't just get her kicked out for her job for drugs or stealing or something. Hack into her computer or sneak into the office or something and delete/ tamper with her work, so she has to work gruelling hours trying to replace/ fix it all, losing touch with the rest of her life, losing sleep, not staying well until, finally, after weeks or months of this, they sack her. *THEN* you hit her with the drugs or the driving charges or whatever, so that she can't get re-employed.
As for drugs... I know speed can make ppl pretty aggressive but I don't know a lot about it (but there's always wiki). I've also seen ppl get really nasty on caffeine, believe it or not. I used to work with this one girl who lived on caff tabs and she was one of the scariest ppl I've ever met. She could flip from pure sweetness and everybody's best friend to hate-spewing *****-balrog from hell inside of about 2 seconds with absolutely no provocation. Looking back on it, I wonder if she didn't have some psychiatric problem.
And as far as screwing with ppl's lives by secretly administering drugs and stuff... I thoroughly recommend you go read "invisible monsters" by Chuck Palahniuk:
http://www.amazon.com/exec/obidos/tg...books&n=507846
You'll be glad you did (although you'll be lying in bed awake for about a month, worrying about the soul of the human race)- it's a fantastic book, I burned through it in two days.