Welcome to the board,
As a Animal Services Officer, I have to say that is it not the best interest for you or your dog, to let her off leash, if she is prone to being aggressive with other dogs. Even in remote areas when hiking. You are pretty much asking for trouble letting her off leash. You could be fined greatly, sued,and worse your dog could be put down. i dont mean to be rude, but please be responsible and leash your dog when out in public. I see and enforce dog attacks everyday. GS and Huskies need regular extensive excercise. Why not give the SPCA a call where you adopted her from and see if they can provide any help? Maybe they have a behaviourist that works there or can provide outside help?
I'm just curious are you experienced in dogs that have aggressive issue? I am a little shocked that a SPCA would adopt out a dog with agressive issues (as a liablity on their side) I mean i know some shelters that, if they have a adoptee who has extensive experience working with animals with behavioural issues, but its rare.
I hope you can find a solution. This dog deserves a second change and it breaks my heart in wondering why your dog has resorted to this behaviour, as I know it probably has to do with her previous contact with humans