I've seen plenty of dogs who went through this sort of stuff come out of it as wonderful, grateful loving pets. They end up devoted heart-and-soul to their new people, because they know
their new people changed their lives. It takes work, patience, and GOOD training (I totally agree on starting with clicker trainer and positive methods for a dog like this--she's had enough pain to last a lifetime). I also totally agree that establishing trust with her will be the foundation for everything.
You might be amazed how fast these dogs leave their old selves behind once they're in a safe, good environment. They often bond very, very deeply with new people. She will probably be afraid of men -- and it can take a long time to undo that. If you are a woman, this will probably be easier to accomplish (assuming all the abuse she received came from a man).
She will probably always be afraid of being confined with a chain, but there's no reason for her ever
to be again. That may translate to fear of a leash, but that's something that great positive training can help with. You may end up needing an easy-walk harness, as dogs who've been abused living on chains sometimes have medical problems in their necks -- and the harness is also psychologically easier for them.
My biggest concern is that I'd like you to have a good trainer help you to evaluate her. If there's a breed rescue in your area, they may have someone with enough experience to help with that too. Your post suggested that she has a history of attacking dogs and humans. These may be defensive attacks, due to the abuse. Or she may have been taught to do it by the abuser -- and that's a Very Bad Thing. You need to know whether she represents a danger to the community (and your household) that needs to be addressed if you want to help this dog. I'd really want you to try to learn more about these past bites of humans, what precipitated them, and the circumstances. This could be a dangerous situation -- or not be one -- and someone needs to help you evaluate the dog to figure it out.
Assuming you get past the evaluation....how do you establish trust?
1. 2-week shutdown. It may end up being longer than that. In the search box on the forum, do a search for what this technique is and how to do it. It's very, very important that you commit to doing it with this kind of dog -- she's been living outside on a chain, knowing only fear, so she needs to be able to have a safe space (crate) in the house to observe and soak the new life in. This is about giving her a transitional period where nothing is asked of her, and she's just allowed to be safe and soak it in.
2. Calming signals. Buy DVDs or Books by Turid Rugaas regarding canine calming signals -- silent body language dogs use to convey "I'm not a threat." Humans can use many of them to send the same message to dogs. I use them a lot with foster dogs. They really
3. Go slow, and set the dog up for success. Don't ask anything of the dog that it's not yet ready for. The healing has to be done at the dog's pace. This means organizing your life around it's stimuli thresholds for a while, then gradually pushing those thresholds a tiny
bit week by week. It's a journey made in baby steps.
The key thing to keep in your mind is that trust is earned
. That takes time for some dogs.
Here's a video a friend made about one of her foster dogs -- an old dog who was chained and deliberately starved. This dog had never been pet or touched with love and, at first, she didn't know what people were even trying to do when they did that. Watch how the expression in the eyes changes and warms over the course of her recovery--her eyes totally tell the story: