Her name in the show is Lila and she becomes Dexter's 'mistress' after meeting him at a narcotics anonymous meeting - she's an ex heroine addict.
In real life her name's Jaime Murray and she's my big sister! :-)
Proof, or it's not true!! She's a good addition to dexter, but my god, she gets really annoying towards the end of season 2!!...
Ah! that would be telling!! Let's just say that Lila does something for Dex to make sure there's a season 3!!...