Wow, I am glad you fired her. I agree that is a big no-no. I've dealt with aggression before and the worse way to to deal with it is by making them fear you. There are such things as fear aggression and it is the hardest type of aggression to overcome. Not to mention using a collar on her and dragging her by it
. There are training collars out there (no, not choke collars) that can be used for correction but her technique was unnecessary and a bit much for a first encounter. I could see using a collar on a larger dog (if necessary) but not a Yorkie. It is way too dangerous.