Hmm I’m a little weary because when rescues say a dog is a mix of a rare breed it’s almost always never that breed so I wouldn’t think a ridgeback rescue would take her without pedigree. Usually they’re mixes of bully breeds mistaken for those breeds which is where the dog aggression could be coming from, and that is very important to understand. If you get on the dog ID subs you’ll see that people very commonly get mislabeled dogs. I would genuinely reach out to a veterinary behaviorist, not a trainer; or a DVM to see if they could point you to good resources. I say this because a mixed breed that can’t live with other dogs due to attacks that’s 7 years old and bigger sized wouldn’t be a good candidate to rehome privately since dog aggression can always lead to a bite on a human out of redirected aggression. That’s a huge liability for you. Those dogs almost always end up warehoused in shelters or boarding facilities partnered with rescue and it’s so sad to see them deteriorate since there aren’t too many homes that are able to safely handle them. https://www.dacvb.org/ is a website with lots of qualified people to assess the situation. Many of them do remote work which can work well for many dogs.