Well geesh, I guess I should never ever let myself be lied to by someone I'm RESCUING a GSD from. I would not have adopted her if the previous owner had been honest with me about the amount of work she needed. She is an adult, seemed pretty well trained and completely fine when I met her and did not show aggression until I'd had her for several weeks.
And did you even read my last post? An unleashed dog came up to US, while my dog was on leash. The only places I let her off leash are places where I'm 100% sure there is nobody else around (currently a new park that is being worked on, that nobody knows about yet, and there's about an acre with great visibility where I can let her run around safely).
I have not gotten rid of her, by the way. Yes I am keeping that option open if things don't improve after several months of training, because I know with my lifestyle I can't give her what she needs if what she and I need is TONS of work. (and I see she AND I, because yeah, I know my behavior is probably part of the problem and I'm going to try my damnedest.) She's already better and I'm feeling more and more hopeful that she'll stay with me. And of course I try to keep her separated from dogs on leash now--again with the not realizing she would react like this on walks because her previous owner said she was fine.
We can't all have partners to help us with our dogs, or lots of money, or lots of free time. I made a choice based on what I was told and I am doing my best here.
Oh the adopt-don't-shop stuff kind of burns me up because they don't tell you the rest of the story. Yes, you can get a great pet that has been given up by someone else, and these dogs do need homes. But a lot come with baggage, baggage that doesn't show itself right away. They are shocked to be in the shelter, and then shocked again when moved with you, and it isn't until they start to relax and get comfortable, that the behaviors that got them chucked in the first place start showing up. And yeah, that can be several weeks.
But the good news is, you have a dog with some quirks, and you are willing to work on those, or MANAGE THEM. You have choices. You need them manage them from the get go, but you can also work on them as you go forward, or just get really good at managing until it is second nature.
I agree that you don't need to and shouldn't allow this dog to sniff another dog. I know this ran up off-lead, and you are going to have to protect your dog from off-lead dogs. If that means carrying an air horn and spraying it toward them to stop them in their tracks. do it. If it means shouting at the owner to GET CHER DOG!!! do that. You have permission to be rude, as rude as they are being and maybe more. Because you are protecting their dog too. So if some one comes up with their totally out of control dog dragging the to yours, while the owner laughs and smiles indulgently and says, "Is he friendly?" Say "No." and move away. Don't wait around to apologize or explain (unless your dog connects with a person). If your dog reacts -- barks at, snarls, puts hair up, take it as you didn't adjust early enough and move in the same direction you were going, quickly with a slight correction or eh-eh and get your dog out of there. Don't worry about nasty looks from people. You are trying to get your dog over this, and the best way is not to let her languish in a bad place, or let her develop ways to get herself out of the situation -- that is your job. She will develop ways you do not like. So, don't worry about being rude, and don't let her behavior turn you around, but do get her out of the situation as quickly as possible, and try to avoid similar situations before she reacts to them.
Hope that helps.