I personally think it was a bad idea for you to tell your neighbor about the cayenne pepper. Now if she notices in the beginning that her dog might sneeze or something, she might blame you for trying to do something to her dog. These types of people are not reasonable. What they do not know does not hurt them.
The dog gets a snoot full, learns its lesson right away, and stays away from that part of the yard. Your neighbor does not, or will not train her dog own dog. She has deemed it YOUR problem.
I am surrounded by three different yards or you could say five yards counting the very corner lots. Some of these fences are old and some are new. My problem was the dogs were not only barking
they were attacking the fences. THEY DO NOT DO THIS ANY MORE.
They are still in their yards and they are still alive. They still bark but that is on the other side of their property and they are barking at someone elses yard and not mine. And they are not attacking my fences anymore. My neighbors are none the wiser.
I did not have to wear a mask to apply the pepper because I was not flinging the powder. I was applying it at ground level or on brick retaining wall "sniff" high. One does not fling cayenne pepper in the kitchen either.
I will not use any product that will hurt me or my animals or anyone elses animals. If you do the research, you will see that cayenne pepper is used in products that you can spray on your vegetable gardens to deter other garden pests.
No one was more surprise than I was that using this pepper has worked. It worked so well and no one has been hurt or upset. I wish you well with this venture. However, be prepared for further problems with this nutty neighbor. Some people will not accept their own responsibility in these matters.