You could drop a two by four infested with termites next to his house (make sure your friend has her house treated first).
You could call the Mormon Church and have a book of Mormon delivered to his house. He would then get incessant visits from missionaries....
She could have any gun nut buddies come by for a front yard gun cleaning party....
Ranchera music on kind of loud carries a loooooong way....
Or she could go over there and politely ask him to leave her the fuck alone.
If she has a friend that is intimidating looking, he could play possesive boyfriend.
She could invite him out for drinks, get him drunk and then when he tries to drive away, call in a DUI airstrike on him.
She could invite him out for drinks, take him home and tell him that "This time, I'm the man!" as she whips out the strap on....
Seed his yard with crabgrass and then call compliance on him.
GT