So, Addie has a history of being possessive of me and snapping at other dogs like at my mom's house, or a friend's. These are dogs she has a history of playing with and enjoying, but more so lately she has become aggressive towards them when I'm around. Fast forward to last week, the boyfriend and I picked up a Lab puppy for his sister and her husband, and are puppysitting him until next weekend. The puppy is a sweetheart, very submissive and easy going. He doesn't even try to play with Addie much less bother her at all. She has gone after him repeatedly now and I just don't know what to do with her. The first time it was because they were in the kitchen with food involved, fine I understand that. The second time she was on the couch, and he was walking on the floor near us. That got me quite a bit more upset. Now, she turns into a ball of obsession and aggression any time he's nearby. She will get so tense she will NOT relax, so we have just been correcting her and putting her up. Mainly because I don't know how to handle the situation and also for the safety of the pup and our sanity. She cannot relax, I feel so bad for her. She has always been an only dog, and she's so very stubborn. One of these days I will want to add a puppy to our house, how in the world do I keep this from ruining her little life and having a house of fighting and separation? Also, more recently she has become kennel reactive and leash reactive to other dogs. She doesn't take correction well. She just comes back at you because she is so wound up. What can I do?! She's just become so unpleasant this past week and I'm upset for her..