You have to prove its UN-Livable space... a simple fake rubber snake or LARGE dead spider carefully placed in the basement will resolve all wants of a lady going to the basement. Let alone living in one.
We had a wounded bat in our fully refinished basement, a mouse, and Gardner snake found over the course of 20 years in our home (It just happens) . All of them my wife found on accident, She has never returned in the last 8 years, let alone wanted to sleep down there. Ah train heaven!