I thought I'd jump in here. My very first dog as a young married person was an aggressive young dog (very dog aggressive and also, to a lesser degree, uncomfortable around people, tending to snap at anyone who was forward/friendly with him). He was an "only dog" at home and this translated into him being a real social clutz, confused about how to act toward strange dogs, especially.
This is what worked for us/him:
1) Classes--I took him to a great obedience class first, with a firm, knowledgeable, non-violent trainer...the class was full of all kinds of dogs, both purebreds and mixes. He was, at first, intensely interested in being pushy with the others (snarling, lunging...it was very embarrassing to begin with but we persisted) and he calmed down after a few sessions. He actually became the *star* of the group, obedience-wise, and learned to ignore the other dogs/be calm around them.
2) Socialization in other settings--with coaching from a friend who bred/showed dogs in conformation, I took him everywhere I could think of, on-lead. She let me come to her show/confirmation class (and had all the other members of the class spend time handling/touching him). I took him to parks, grocery store parking lot (letting people pet him all over, with me holding his collar/head carefully, asked them give him one of his favorite treats after touching him). And I took him on walks down neighborhood alley ways--this was ideal, because all the other dogs would come to their fences in a rush, barking and snarling at him, and he would want to tear their faces off! But there was a fence to protect everyone concerned. I carried a spray bottle of water and sprayed him for any reaction to them. He hated water in his face and so he soon figured this out. If he was calm, I would let him go over to the fence to "meet" them. But on any sign of aggression, I would spray his face. I also had him on a choke chain collar (*never* use anything nastier). This was always placed up high behind his ears, and I used a quick, sharp pull if he was aggressive to the other dogs, not long, strangle pulls. I didn't care what the other dogs did, just what he did. I talked to the others pleasantly, never yelled. I talked to my dog, teaching him cue words, like: settle, no pull.
3) I found an open-space, remote area where I could run him off-lead with no other dogs around. I worked with him on "come" and made sure he was tuned in to me off-lead. Eventually, we'd run across other dogs at this setting, off-lead too, and I discovered that he was much more a gentleman with them when both were off-lead/on equal footing. He had less of a problem with other dogs when they were both loose, but if a stray dog ran up to us while he was on-lead, he would become defensive/aggressive, nervous about their intentions and well-aware that he was "handicapped" by the leash. I sometimes would let him off leash at that point and he and the other dog would "posture" and perhaps chase around a bit or even play.
4) Patient work on the above, daily "social exercises."
Dogs *can* learn to control themselves and in our society, they *have* to. You don't want to hide your dog away or live in fear of risking injury, vet/medical bills (which you will end up paying!), loss of friendships, fear of lawsuits. Classes and training do take a little time and money (though usually you can find an obedience course at low cost--try through your community recreational center if you have one or Chamber of Commerce or vet) but if you truly love your dog and want to prevent injury/trouble/expense, it is wise to take the time to do what is needed.
4) Doggie companionship. When we added a female dog to our household, we saw a strong positive change in his attitude and social ineptness. It helped that the new dog was very mellow, non-aggressive. She helped him feel more confident, I think, not so alone.
***Our dog became the nicest guy over time; it took a few months to see good progress and maybe a year or two to ultimately feel confident in him and for him to "grow out of" it, as well. Mental maturity plays a part, but you need to structure their learning while they are growing up so they figure it out *right*! I eventually began running him in field trials and he *never*ever* had a problem on the field with other dogs! He soon became a field champion and he was dubbed "Mr Mellow" by the other trial owners. I was often asked to let him be a "trainer dog" for aggressive field dogs in practices. Some of them actually tried to attack him while they were out on the field together, but he would look over his shoulder at them like, "What's your problem? Get a life!" and run on!
Good luck--insist on good behavior from your dog and give her the coaching necessary to help her succeed.
Rosemary
