I got Ramona when she was 14 weeks old. She is my shadow and absolutely bonded to me. I am a SAHM so we are always together when Im not out and about. She is so sweet, a kind but shy disposition. I clearly havent done enough building her confidence. Shes wonderful at home, on leash or off leash. Shes amazing with my children and any kids or friends who come to visit inside our home.

She is now 8 months old, and I have had 2 scenarios where now I worry I havent done enough and I need advice. (I already reached out to a professional trainer and am waiting to hear back) about a week ago I went to take her to the vet, she was nervous but good until the vet tech and vet cornered her then said she needs a muzzle because she's so big (I already found a new vet) and then when they wouldnt let me get her out of the corner she did a little air nip at the vet tech. The vet said it is my fault she is like this and refuses to see her (this vet also didnt like her and told me I was going to make her aggressive by loving on her too much, its a little old lady vet). I was horrified because Ramona had never acted like that or done anything remotely reactive or aggressive before. As soon as the vet and vet tech left the room she was back to fine and when we went out to the front area the admins were all loving on her and she was fine with all the other dogs and people going in and out. (I stuck around for like 10 minutes after that happened to try to turn the situation around for her so we didnt end on a bad note). 

Just a bit ago I was walking her alone on the trail near our house when my neighbor, 39m crossed through the trees between the trail and his yard to say hello, she has seen him before but only up close when we first bought our house 2 months ago. When he started to get close she got between me and him, hackles up and growled. NEVER has she done that before. As soon as I told her to stop and he and I sat and talked for 15 minutes she stayed quiet and laid at my feet, but he did not get any closer and she also didn't have any interest in trying to get closer to smell or meet him despite me telling her he is good and a friend and gave her some pats while I talked to him. 

I realize this is part of why I got her. I do feel safer with her, but after the vet telling me I will ruin her and cause her to be aggressive I am terrified she might be right. I love my girl and the last thing I want to do is put her in a situation that will end badly for her. 

I guess I am asking for advice on how to curb this sudden protective aggression. Or how to at least help her know the difference between a stranger or friend. I contacted a trainer and am waiting to hear back but any advice or training tips is appreciated.

Ive started working on muzzle training and extra protective measures. 

To add also, she is fine when I leave the house. She is crate trained and is happy and feels safe in her crate. She is not destructive or crazy. She's truly an excellent dog in the house and with my family. 

Please dont admonish me, I fully understand I have made mistakes but I am trying to address them immediately to avoid any future problems. No she is not my first dog, but first guardian breed that is directly my dog.

Scared Im ruining my dog