She is beautiful! Chloe's looks are pretty much on the Retriever side, but that white patch on her chest could be from RR since I don't think the retrievers have that, and I can maybe see a bit of it in the upper part of her face. She is much thicker, with thicker coat and tail than an RR. Her legs look a bit on the longer side so that could be from RR too. Personality wise I hear a lot of Ridgeback in her though haha! In the rescue, dogs are not considered RR unless they have a ridge or are very obvious in their cross. It won't hurt to treat her as an RR though since you are making that judgement on her behaviour and not her looks.
You are right in that you will never have the type of dog that your GSDs were. They are a working dog and have a tendency to be more obedient. Ridgebacks were bred to think for themselves and make decisions, and this is what they do! Also, you are right that getting angry and being harsh doesn't work. This does not every work with RRs. Since you are a horse person (me too), look at her more that way-they particularly remind me of Arabian horses. They need understandting, gentleness, CONSISTENCY, boundaries, LOTS of exercise and human attention, and firmness.
Where in ON are you? If you check out the CKC list of Ridgeback Breeders, you might find one sort of in your area. If you have any particular problems they might be able to refer you to someone who could help. Hopefully the dog trainer in your area uses positive reinforcement training, as that is what works best with these guys (as you've noticed and are working with by carrying treats!) You're right though, the exposure to other dogs and people in a controlled environment will help. Good luck with the classes!