Nope, your dog should be fine. Very small portions of chocolate aren't typically toxic to dogs, and since it was only a dime-sized portion, there's no need to worry. In fact, I've known some breeders who use M&Ms as treats in the show ring! I wouldn't advise that, but it just shows that very small bits of chocolate won't kill. If your dog ate a whole bar of chocolate, then I'd be worried, but she should be fine (and probably happy from eating some yummy icecream!).