Guarding/territorial/fear aggression?

[eotto]

I have a 10 month old female German Shepherd. My fiancée and I have had her since she was 6 weeks old. We have taken her to pet smart obedience classes and currently have her in schutzhund training. We have taken her to the dog parks and she has been socialized with other dogs/adults and interacted very well.


Within the past few months, our dog, Scout, has become very aggressive in our house and in my parents house. She is constantly barking if she sees people outside the window and does NOT like strangers. If guests come to our house she circles them and barks and does not let them get anywhere near her. However, when we go to the dog park, she is fine with everyone and lets everyone pet her?
Within the past two weeks, she has snapped at someone and bit my brother. We took her to my parents house for the weekend and my brother was there, he was trying to make friends with her and he was feeding her treats and then all of a sudden she growled showed her teeth and bite him. The bite was pretty nasty and his hand is bruised and swollen. I felt absolutely awful and immediately got my dog out of the house. This was a wake up call but I'm at a complete loss. I'm not sure if she is trying to protect herself or protect her territory. This was only the second time she had met my brother and the first time he got scared, ran away from her and she chased after him.

Scout also does not like kids, I have a younger brother (12) she absolutely loves him but she has known him since we got her. Scout growls and barks at all his friends when I take her so I have to keep her on a leash so she doesn't go after them.

Once again, this behavior only occurs when we are at my house or my parents house. Please let me know any suggestions, we are currently seeking some type of animal behaviorist to see if they can help.

Sorry if this is a repost!