Since Bella was a shelter adoption, you don't know exactly what happened to her before you came to her. It is possible that the vet reminds her of someone who was mean to her. I am glad that she is not mad at all vets or all men. That can happen if there was abuse that you don't know about. Just keep her on a leash and at a safe distance from your friend the vet, you might give her another chance to see the vet--the best way might be with a fence between them and he can just talk quietly with her. If she freaks, don't try to have them together anymore.

We tried to adopt a dog who was on her third home. She was going to be put to sleep the next day. We brought Sally home and things went pretty well for a few months. She did not like my husband because she had been abused before, but she tolerated him. One day she tried to bite him when he told her to go outside for a potty break before bed. We had small kids and I realized that we could not keep Sally and risk her biting them for no reason. Sadly we took her back to the shelter--I don't know if they tried to adopt her again. Abuse can stay with a dog and come back when they see someone who reminds them of the abuser. Since Bella only has one person she does not like, it sounds like you should be fine. Let her tell you who she wants for a friend.