Wilson proclaimed her "principled" support for assisted suicide in a BBC documentary, but this week rejected a challenge to return to New Zealand to argue her case before the High Court.
In emails to the Herald on Sunday she said she would not return because she was ill from spider bites which caused her to sleep "almost 24 hours" a day. She also suffered from "brain attacks" triggered by too much adrenaline or certain odours, including perfume and hair spray.
"Being in a courtroom would be quite stressful for anyone, and I am already taking quite a lot of medication to stop the effects of adrenaline," Wilson said. "Any courtroom I would be in would be full of medics the whole time."
She said her life had been a "sentence" for 18 years because her illness prevented her from socialising. Her only companions are a pet lizard, a bird and cat. "Why bother going through so much effort to have someone tell me that I have to live like I am already forced to? I no longer go to the places I used to enjoy. I quit going to restaurants because I would fall asleep, and then up in bed."
Wilson claimed Wallis would similarly have helped her if the tables were turned.
"Audrey would have done the same for me if I had asked her to be present while I exited, and I would have helped her with her travel expenses as well."