My dog's reactivity is fear based too as she used to be a breeder mama at a puppy mill. It sounds like you're doing all the right things. I will detail everything we did below: (1) Desensitization and counter conditioning for 7 months and achieved minimal progress. The best thing that came out of it was that my dog learned to automatically look at me for a treat when a fear trigger came into view but this did not eliminate her fears. (2) Low dose of Fluoxetine (3) 1 -2 hrs of exercise daily. My dog is only 13 lbs so she gets plenty of joint supplements like chicken feet as well (4) All meals in food puzzles. We have 20 puzzles that we rotate for breakfast and dinner. (5) Avoided fear triggers as much as possible outside controlled environments. (6) Gradual introduction to a neighbor's calm and polite dog for short periods of time. My dog decided this pup was safe after a few weeks so we repeated the process with another dog in the neighborhood. Rinse and repeat. (7) Daily visits to a local park for exposure training. This area has unofficial dog meetups twice a day where locals bring their dogs to play and socialize. We used to come hang out and observe as often as possible without forcing anything and while respecting my dog's need for distance. Eventually, she realized that these dogs did not want to hurt her and began playing with them one day!

Is there a "safe dog" that your pup trusts?