I'd get a metal detector to look for sunken iron posts marking the property boundaries, and the plats for nearby houses, and satisfy yourself about the boundaries. A telephone pole distributing elec. power is a likely boundary candidate. You may also want to rent a transit and a long steel tape.
Try to find out if your neighbor lady is chronically litigious, as people with a Paranoid Personality Disorder tend to be. Check the courthouse.
I guess you could also send her a bill for your labor.
This broad search may possibly be helpful to you.
http://www.google.com/search?client=...UTF-8&oe=UTF-8
Using Google's Advanced Search option comes in handy, too.

