Working in a university was a relatively supportive environment.
"In 11 years as a lecturer, I have never been misgendered," she said. "Well, actually there was one time when an Indian student called me 'Ma'am' and 'Sir' in the same sentence."
But in 2007 a police officer stopped her car, although she had not broken any law.
"He said, 'Get out of the car,'" she said. "But I'm a bit deaf, so I said, 'Can you sit in the car with me? Or if you like I can sit in your car and answer questions.'
"I was attacked by this cop. He hit me, I hit the ground. He grabbed my hair, smashing my face into the concrete.
"I was arrested for obstruction and resisting arrest, which I quite simply hadn't done. I had to go through the indignity of being searched by a male officer in front of other officers, my glasses were taken off me."
She was put in a police cell with several men, and later went to hospital with concussion. She had to fight through the courts for two years to get the charges dismissed.
Thirty years after homosexual law reform, three years after same-sex marriage, New Zealand's transgender community is still waiting for equality. Efforts to add "gender identity" to the list of discrimination in the Human Rights Act, by MPs Georgina Beyer in 2004 and Louisa Wall in 2014, have failed.
But for Ms Matheson, becoming a woman has been "a lifesaver".
Sexually abused as a child, she struggled all her male life with bipolar disorder, swinging between extreme "highs" and "a very deep hole".
"What went with the [gender] transition was the suicidality," she said. "I was driving back from the North Shore after speaking to my counsellor and realised I hadn't had a suicidal thought in six weeks. That has been maintained."
The sporadic depression continued for several more years and ended in a surprising way: she and her partner Cushla took up karate to support their son Finn, who was conceived before Ms Matheson's transition and is now 13.
"I did one class, and I couldn't walk for four days, but I had such mental clarity at the end of that class that I thought, this is worth it."
She now has a black belt, is writing a doctoral thesis on the history of karate in New Zealand, and said: "I haven't self-harmed for years, because karate gives you a sense of yourself, a sense of who you are, a sense of self-respect."
