Well, since you asked for opinions I'll go ahead and add mine.
To be completely honest I think you are overreacting a little bit. I'll explain. Yes it was completely rude of her to laugh and I would have been a little ticked off as well but in all reality, her dog was most likely just playing and your dog was probably absolutely fine. Dogs play extremely rough. Even now, even though I've owned dogs for years, I still am tempted to break up Franklin and Maggie playing because it can get really rough. I always forget that they don't have really any other way to play besides jumping at each other and biting each other. Secondly, a 5lb difference isn't really that big of a difference, especially since you said your Yorkie was larger. Franklin and Maggie are 9 and 11 lbs and I let them play with much larger dogs at the dog park without any problems. The owner probably didn't realize you were upset because she thought the dogs were just playing. Since they were probably just playing, she had no idea they would do that. It wasn't as if her dog bit yours and she knew it was aggressive and brought it over. Does that make sense?
I agree with some of the other posters... I would never touch another person because their dog accidentally hurt mine.
