AS YOU PROBABLY KNOW CHOCOLATE IS A NO NO FOR DOGS, BUT THAT LITTLE BIT IN HALF OF AN OREO SHOULD BE HARMLESS. MY DOG HAS GOTTEN INTO CHOCOLATE ICE CREAM AND WAS FINE. JUST MAKE SURE THERE IS A LOT OF WATER AVAILABLE.
She should be fine, if she's got a strong immune system.
I wouldn't let her eat chocolate anymore though, it's poisonous for dogs apparently. But no, once won't hurt.
