I have a 12 week female Corso, Xena. She has been doing really well with people and dogs, showing no fear or aggression to this point. The first time at the vet at 8 weeks went really well and she was happy. I have been taking her to other people's houses that have kids and dogs and again no issues, except for some fear of bigger dogs but no aggression, just kinda sitting between my feet until she is confident enough to greet the dogs. Well, I took her in for her second set of shots and she would not let the vet even come close to touching her. Serious growl, the vet attempted to touch her and Xena snapped at her. She was muzzled at that point, her mood did not change until we left the vet office. I took her over to a friends house afterward just to see if she would repeat the behavior there but she didn't she was happy, playing and greeting everyone. Is there something I am missing. I have not taken her to dog parks as she has not had all her shots so I'm pretty limited. She will be starting obedience classes as soon as she has her next set of shots in a month, but I really do not want to get kicked out of class because of aggression if that is what she is showing. Any advice on what may be going on or how to further work with her without exposing her to too many illnesses before her shots would be greatly appreciated.