Donīt really understand that decision but she probably thinks that she needs a break now after her matches in Wimbledon, a shame, would have liked to see her in Stanford, she still needs matches!
Apparently Sabine is trying to keep this under the radar:
Pennetta/Schiavone (ITA/ITA) d. Hsieh/Lisicki (TPE/GER) w/o (Lisicki left abdominal injury)
I'm sure she has enough class and wants to avoid any hint that she would use this as an excuse for her collapse yesterday, but it would explain why she took a longer break than Angie after the second set and just didn't look right during the entire third set -- especially now that it is apparently serious enough to withdraw from Stanford. I seriously doubt she is just "resting up for the Olympics" and I hope it will heal before then. This appears to be a recurrence of the same injury she suffered against Angie in the quarterfinals of Auckland.
Hopefully she will have better karma with Angie on the same side of the net.