I have a few reasons why it's most likly temporary
Yeah I was thinking along the same thing. I have a feelinng it's temporary. For sevreal reasons. 1. The actress who plays Ahsoka is recoring Season 4 and says she feel's that Ahsoka is far away from the Darkside.
2. Anakin wouldn't have gone to the Darkside if his Padawan went because he'd pry kill her.
3. Previews are sometimes meant to throw you off.
4. If you look at her face in the pictue at the bottom her face is covered with something as if she has the Blue Shadow Virus again or something of the sort. Or something like the Geinosain brain worms that haunted the Clones and Barris. And look how her eyes are yellow, I know this happened to Anakin in Episode III but that might be a not so good change. We don't know but I think it's temporary.

Thats really sad!!

actually the reason her face was like that was because that is what happens when someone turns to the dark side as showen in the games kotor 1 and 2. but i think its only temporary i think she will turn back to the light side

i highly doubt that she is turning to the dark side for good i'm pretty sure she is possessed by something i mean someone can't be completly good and then all of a sudden go to the dark side just like that and its to early in the show for something that drastic to happen so i don't think she will be dark for long

What I think is she gets brainwashed by the nightsisters because she's a girl and they probably think she's powerful because she is the Chosen One's padawan. That's my prediction.

No she is not. I reckon she's gonna die because the writers will have to kill her because she makes no appearance in Star wars episode three, four, five and six. And she should die, itd make the whole thing way more realistic and cool. I'll be pretty sad if she just stops being a jedi or some stupid crap like that.

Well no DUH she doesn't appear in episode three, four, five and six! This is the Clone Wars series we're talking about here! And, we already know, she's not on the dark side anymore. She was just taken over by the Son. After she was killed and revived, she was back to normal! Where have you been?