I agree with the training frequencies.
First and foremost I am a dog lover and it is not the dogs fault that he/she barks continuously. Dogs will do what is natural to them unless trained to do different. The problem is the pet owner and not the pet.
Pittbulls are very emotional animals have a natural separation disorder. They will normally chew or bark unless trained otherwise. I will go out on a limb here and say they are one of the most misunderstood species of animal on the planet.

Work with the frequencies (there's an app for that) and if you cant dial it in then talk with a local trainer. Offer the neighbor the trainers info and prices and kindly let them know there are only two things you can do at this point and you are taking the high road for now. The step you are avoiding involves law enforcement and all you really want is what is in everybodys best interest including the dog.