TMTT, I see three options.
1, here in Illinois, there is an air-line boundry. Anything that is in your side of the line is yours. Cut the tree straight up from your line.
2, Make friends with a lineman, (but keep it quiet ), they have a chemical that they put on the ground that will kill it with-in a year.
3, find her weak points and ride them, make her sell and move!!!
I had a neighbor that was a night outdoors drunk. He would get home at 1 AM and turn his outdoor speakers on and drink. I needed my sleep and the Cops were not very good at keeping the neihborhood quiet. On night there were 18 calls about his stereo-all different #'s. When I call , the dispatcher named the song with my windows closed!!!
So I checked the local ordinances, and built a fence. Nothing on the books. It was 8 ft high with sound insulation on his side. Shiney side to him. It really made a difference. He spent the next 2 years trying to make me take it down, no luck. he moved. I bet 75 people thanked me!!!!