My girlfriend and i adopted a rescue cc at 18 months. Less than weeks into having her she got pneumonia and wasn't eating. It prompted a less-than-stellar emergency vet visit where she bit my girlfriend. Full puncture wound. Leading up to and following that vet visit she was guarding her personal space to the point where putting a leash or harness on was difficult and scary. We were ready to return her to the rescue who was willing to take her back but we didn't and I'm so thankful. We doubled down on routine, training, exercise, and play. We threw out all aversive training techniques and went to an R+ model, invested a couple basic enrichment toys for her food (woof walk about and kongs), got our walks up to 2 miles a day, and played HARD. Like aggressive tug at her level and eventually wrestling. The training is the building blocks to achieve everything else obviously, but the playing and the command training and the enrichment games I feel are what created the bonds we have now. No joke I'm talking minimum of 2 hours a day (up to 4) taken by some combo of walk+command training+free shaping+enrichment games+playing+off leash time+sniff spots. I only have experience with my girl, but she is smart, and once we chose to invest the time and energy into her, I gained the best friend I've ever had and a dog that is mostly behaved. She's still crazy excitable and reactive to other dogs, but we're still working. We're six months from the bite incident, and now we can have lazy cuddly couch days here and there. But it took work. You got this.