Aggressive Dogs.

Question
I have a 7 year old female german shepherd who has always gotten along with other dogs. She would play with dogs and cats, until she had puppies about 4-5 years ago. After she had puppies she became quite aggressive and overprotective. I bought a 13 week old german shepherd last night, male of course, and now I am scared to intorduce them. When the male was brought into the house, she was sniffing him and jumping towards him, since he was being carried. Nowhere did she show signs of aggression. Her tail was wagging, but, at one point she did growl. Now I am not sure if this was such a good idea. We have kept them seperated, due to the fact that we're scared of what could happen. This morning we took the male to one side of  the gate and the female to the other side of the gate. We let them meet, sniff each other and even lick each other. There was no growling or barking, just a lot of wimpering and the female was digging under the gate to try and get at him. What would be the best way in helping them meet? Would it be to put a muzzle on her and let them around each other, but then I fear what could happen when the muzzle is off... or, what else could we do? Put her on a leash and see how she reacts towards him? Any adivce would be greatly appreciated.

Answer
Having them meet through the gate was a very good idea. It's much better than the leash because the leash can frustrate dogs. I would do this several times a day before you let them meet so they can get used to each other and give your girl lots of treats and praise while he's on the other side of the gate. You can also put him in his crate and have her sniff him in there a bit before they meet without barriers.

If you are really concerned you can keep the leash on her or even muzzle her for their first face to face meeting, but that will add more stress to the meeting and you don't want her to blame the puppy for the muzzle. I'd put a leash on both, but let the leash hang so you can just grab it quickly if need be. If she has shown no sign of aggression thus far, I suspect it will be okay. I would have them meet outdoors in an open but fenced area or in a large indoor room so there is plenty of space for them to get away from each other if need be and stay close so you can swoop in for the rescue if you need to. While she is being friendly, praise her and pat her and tell her how good she is. If she growls don't punish her, but express your displeasure.

Many dogs who have issues with other dogs are usually fine with puppies provided they are smaller. Large puppies with their oafish ways and lack of discretion annoy smaller adult dogs but larger adult dogs usually tolerate them well. Since you have raised pups I suspect I don't need to warn you that there is likely to be a little bit of growling and snapping and puppy yelping while they get used to each other but as long as the pup can run and she doesn't pursue him, it's nothing to worry about.