My sister has a 5 year old German Shepherd named Maggie. She has a very interesting personality and I am wondering if any of you might have any insight on this. Maggie is a one-man dog, and really responds the best to her dad (my BIL). To my sister, she doesn't always respond. She will often have to be told more than once, and can't be trusted off leash if anyone other than my BIL is calling for her. She is also very aggressive towards anyone she isn't introduced to without her dad around. When we got Aspen, my sister was very worried that Maggie would not like Aspen. I should also mention that Maggie is paired with Chester, my sister's other dog, who is a 7 year old Westie. When we had Maggie and Aspen meet for the first time, everyone just remained calm and Maggie and Aspen got along great. She had a few warning growls here and there, but other than that, they got along just fine. Now, fast forward 10 months, Aspen and Maggie are great friends. They get along so well and love to play together. My sister thinks it's so odd because Maggie truly does not like any other dogs. Now this is the part we are really confused about. Maggie would protect ANYONE she loves if they were getting hurt. However, there have been a few incidents with her being aggressive over toys. There was an incident that happened maybe 3 years ago when I was watching Maggie and Chester, pre-Aspen, and Maggie grabbed Chester by the neck and shook him around like a toy for about 5 seconds. I was horrified. She has done that maybe 2 times. That hasn't happened since Maggie was 2. (She is now 5.) Now, I will watch all three dogs when my sister goes on vacation. There is a dynamic between them all that concerns and confuses me, so I keep them separated. Chester, the Westie, does not like Aspen. Aspen is much too puppy for him, so we keep Chester in his own space. If, however, Maggie, the GSD hears Chester growling, she will growl and bark at Chester. If my sister is here and they aren't separated, Maggie will cower over Chester and growl at him. My BIL has not witnessed this behavior as he is away from home for months at a time and even I rarely get to see him. You take Aspen out of the mix, though, and Maggie has no problems with Chester. Sorry for the long post, and I don't know if anyone has any answers, but I thought here would be a great place to ask.