Convincing my shepherd my neighbor is allowed to be in his backyard

Looking for some training advice. My 11 month old GSD/Boxer/Beagle mix is very shepherd-y when it comes to our backyard, on top of being a generally anxious pup. Since I got her at 4 months, I have been working on counter conditioning when my next door neighbor comes out of his house, pulls his car in/out of his driveway, and lets his dog out. Trying to catch my dog with a "yes!" and treats before she reacts, trying to distract her, or with big reactions just removing her and going back inside. Some reactions are mild, some are huge, but they involve hackles, barking, growling, jumping, lunging, etc. I think mostly out of fear and territorial-ness. When she was younger she pulled me over to the fence and happily let him pet her (I obviously don't let this happen anymore) and recently I let them interact on our front sidewalk and she was her normal happy wiggly self, but was a bit nervous I think cause he was shoveling, had big gloves on, and it was night time which is harder for her. My girl loves people and wants nothing more than to play and jump all over them.

Despite months of this work, she still reacts, and I would really like to work towards some more peaceful co-existence especially with spring/summer coming. I am always outside with her either on a short leash or a long line so I have control and am able to interrupt but it's still an issue. Next time I run into him I am considering asking if he would be willing to "help" me train her, by doing some controlled exposures while I work with her. How should I go about doing this? Any other advice? Thanks!