I see a lot of responses to contact animal rescue groups, and I will tell you that most of them, including the humane society, won't take a dog that has bitten. I have been looking for a home for a dog that is not great with children - he's very dominant with them and will growl, bark, etc. He has bitten my daughter once, though not seriously, nor enough to break the skin. As I've looked, there are no groups that will take him.
So, while it's very well to tell someone to find a rescue group to take your dog, it's not always realistic. I would call "Adopt-a-Husky" or German Shepherd Rescue today and see what they say. Their information is below-
Adopt-a-Husky
# P O Box 27, Albertville, MN 55301
# Phone (voice mail): ###-###-####
German Shepherd Dog Club of Minneapolis-St.Paul Rescue
Marilyn Lindsey-Miller, PO Box 574, Willenie, MN 55090 ###-###-####
But then, if no one will take your dog, you should not feel guilty putting her down.
My next door neighbor's dog attacked me several years ago. I was the first person she ever bit, but I wasn't the last. You can not ever trust a dog that has bitten, and your son is too young to establish dominance over her. In the meantime, I would keep her either in a crate or muzzled when she's in your house.
I wish you a lot of strength through this ordeal.
Good luck -