Yes, she does have a forehand slice/squash shot (as Jack mentioned). And I've seen her use it to good effect.
Unfortunately, Petra has no confidence now, so she will only use a shot like that when she's drawn to the net, or side line and wants/needs to end the point quickly.
She certainly won't use it offensively, or to set up other shots.
FYI: Vika just started using various slices. But I still don't see her use that shot much, mind you a back hand slice (though I have seen some more from her recently, and heard her discussing net play and variety, after Petra whipped her ass in 2011 multiple times and at YEC, using variety). That's where it came from. Good for her.
As far as Vika winning that tournament over Serena, when they were both playing like shit??
I know it's got some of you mad, and I thought about the same thing. But slightly different way than you guys.
I just thinking how bad the WTA is right now/altogether, that a below standard Vika and Serena, were able to bull shit their way through to the finals. That's crazy!
Cincy, was the perfect tournament for an inform Li Na, Petra, Sharapova, Bartoli (we know she didn't play), Aga (though she tried against Rena); hell even a Wozniaki, Lisicki or Ivanovic to had taken them down. But they didn't!
Instead, we were subjected to awful play through out the tournament, and in the finals (minus some good play here and there), from both.
Rena was horrendous during the 2nd and third set. And Vika was equally horrendous during the first, and had her moments, of both good and poor play during the third.
So where was Petra and the others we ask indeed, to clean up in their well played (Serena and Vika's) absence?