My dog is a lab breed mix and the other dog, I'm not sure.
I understand about not breaking up fights, but problem is this wasn't really a fight, but a dog attacking mine and my dog doesn't seem to know how to defend herself. We've never been in this situation though. I guess she didn't understand or know what to do. She rolled on her back and started yelping. This dog looked like a kind of mutt too, not a specific breed but your average looking, average sized mutt. I don't know what that dog would have had in it at all, hard for me to tell but nothing distinct.

Thanks to everyone for their kind words. My dog may be big but she's just a big soft baby with not a mean streak in her.