Since I said somewhere that I'd post this theory after I posted Part 2 of that crossover that I wish I'd put a shorter title on...
Just a theory about the new blond from 3.01. Note, theory. Not based on anything but what has been aired to date in North America. NO SPOILERS, JUST THEORY.
Please please please do not put any spoilers at all in comments. See sidebar for definition of spoiler.
I am thinking the new blond girl is some kind of hell-sent bodyguard for Sam the "Boy-King" to keep him from getting offed before he gets his demon-blood-fed-baby-psychic mojo up to speed, as arranged by YED before his demise.
Which to me would explain everything, including why she's following Sam, how she's just there all of a sudden and then gone, why she's such a poser, what's up with the magic knife and how can she have such a complete lack of qualms about slashing people's throats just 'coz they're possessed. If that's true, besides bodyguarding, I suspect maybe she'll be nudging Sam towards the 'Dark Side', one way or another, which works in with the predictions I had for season 3, so yay!
And, if all this turns out to be the case as revealed in the fullness of time... I think I might really like the character.
*sits back and trusts Kripke*
Again, if you know any spoilers that confirm or deny this theory DO NOT POST THEM HERE, PLEASE!!!