1. My dog bites, don't touch her. (Saying she's scared makes people want to coddle)
2. My dog is in training as an assistance dog. Please don't pat her as you will destroy her training. (This is allowed as long as you DON'T try to get her into places where a dog isn't allowed, such as shopping centres etc)
The other option is to stand between Dora and the person and tell them rudely "I already asked you not to touch my dog. Go away now, you are scaring her."