Each dog responds differently to a silent whistle and the frequency. Most whistles are in a range between 5400HZ to 12800HZ. You will need to try various ranges (by tuning) to see what makes the dog respond.
Let me know if you need more help.
Typically, the higher the frequency, the more annoying/stimulating it is. But each dog is different. Some dog will go crazy at 5400hz. While others will not.
There is no definitive answer for this.
The whistles are usually used to teach the dog commands. Each "ring" would be given a different meaning. They are not typically used to make a dog bark.
If her dog is a making himself a nuisance and she refuses to do anything about it, you do have some recourse.
First, write a letter to her and send it registered mail, return receipt requested. This way, she will have to sign for it and cannot deny that you sent it. Very nicely, state your complaints and ask that she remedy the problem.
If she still refuses, call animal control in your city or county and report the dog as a nuisance. You can even set up a surveilance camera to video the dog and the fact that he is in your yard, making a mess and threatening people.
If you follow legal methods, animal control is obligated to help you with this problem.
You have to keep in mind that it's not the dog's fault. He's being a dog. It's uneducated pet owners who are the problem.
I don't think the whistle will do what you hope.