Suffering from panic attacks and anxiety, she hit her low point in May 2014, when she began striking herself during arguments with her husband Dave. On one occasion, she bruised herself while hitting her face in full view of her daughter.
"I hit myself. I'm on the floor, raining blows on the side of my own head, and then smashing it into the ground," she wrote in the memoir.
"I'm screaming, crawling up the hallway, sobbing. I've lost hold of my tenuous grip on myself, become something wild, animal."
The young MP returned to Parliament with a swollen face and bruised jaw, and lied to her Green colleagues that the injuries were from a wisdom tooth operation. She told her family, who knew her teeth had already been extracted, that she had hit her face on a car door.
Walker never received an official diagnosis, but is now certain she went through a period of post-natal anxiety and depression for at least two years.
When her husband's muscular dystrophy worsened and made it difficult to look after Esther, Walker decided to quit politics.
She concedes that she "charged blithely into parenthood" against the advice of friends and family, but said she wanted to demonstrate that women with families could have a successful career in Parliament. Instead, she left Parliament "humiliated" by her failure to achieve this.
"I had set myself up publicly as a model of modern motherhood, but the picture of calm competence I was trying to project into the world was a far cry from my private experience.
"Stepping down was like admitting I had been lying."
Walker, who now works for the Children's Commissioner, acknowledged that her circumstances were unique. But she bemoaned the "rigidity" of workplace expectations at Parliament which prevented women from having children when they wanted to, or forced them to compromise on how they looked after their children.
Walker had 16 weeks' paid parental leave approved by the Speaker at the time and was allowed to leave Parliament on sitting days at 6pm instead of 10pm. The Green Party also lightened her workload.
But she said these temporary accommodations were "not compatible with ongoing care responsibilities" and that under the current system MPs had to "either outsource or avoid care responsibilities requiring significant time and emotional energy".
The book lists just four women MPs who have had children while in Parliament and stayed on for more than one term.
"Of course, many women (and men) simply do not want to have children," Walker wrote. "But for those, like me, who want to stay in our careers, have children, and parent them in a way that feels right, things need to change."
The Whole Intimate Mess by Holly Walker
Published by Bridget Williams Books, June 12
$14.99 print, $4.99 ebook
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