She started running away and discovered alcohol, which ruled the best years of her life.
"I started drinking meths and plonk when I was probably 10. I was a state ward at a girls' home. That's when it got nasty," she says.
"It was an evil place. I can remember I ran away all the time, and they used to put me to bed with no pants on so I wouldn't run, but I used to rip the bottom off the pillow cases for a skirt and bugger off anyway."
She had no formal schooling. "All I did was drink - run away and drink, run away and drink," she says.
"A fair part of that time I actually slept in the railway carriages at Quay St and in Pigeon Park and Myers Park and anywhere else that I could hide, because it was actually a criminal offence to be in that predicament.
"There was a lot of food thrown away back then. We always used to find a lot of food in the rubbish. I used to wash my hair in the basin at the ferry terminal and shower at the Tepid Baths."
The worst came when she was sent to what was then the Arohata girls' borstal near Wellington.
"They used to make me scrub the floor with a toothbrush and this screw used to beat me and I'd land on my guts," she says.
"Most of the girls I knew died before they were 25 from overdoses, suicide, self-harm.
"When kids go through that, it's with you for the rest of your life. You end up being uneducated. You are a non-identity, you don't fit anywhere, you've got no family. You go through your whole life and you can't trust anyone. They kill your trust."
She found work in laundries and sewing factories. After work she drank herself into a nightly stupor.
After she moved in with Mr Underwood, she became an "outworker", sewing uniforms for the likes of traffic officers for up to 120 hours a week.
"I didn't want to stop drinking. In the last year of my drinking I was down to a 26oz Coruba a day, a 112oz brandy a day and anything else I could get my hands on.
"The last year of my drinking I was covered in abscesses; they wouldn't heal. I was vomiting up blood clots, I'd swag half a bottle of rum in one go and next minute all this blood would come out. I could hardly move in the end. I had all this pain in my back."
Finally she went to Alcoholics Anonymous, where two longtime sponsors drove her recovery. "They used to boot my backside because, they said, 'I see myself in you.'
She had her last drink on Good Friday 31 years ago.
"It's the hardest thing I've ever done," she says. "You have to do it one day at a time, even an hour at a time."
Mr Underwood was a key support. Asked how they met, she says, "We were just good mates." She says it has been a wonderful relationship: "We never argue."
Ms Henry threw herself into saving others. She still has people struggling with addiction who turn up at her house or ring at 3am.
That soon morphed into advocating for tenants. She founded the Housing Lobby in 1987 to fight state house rent increases, and fought market rents and state house sales through the 1990s.
Oddly, she counts former Prime Minister Rob Muldoon as "really supportive". By the late 1980s he was still MP for Tamaki, and she worked with his office on housing cases.
Through the first decade of this century, she fought against council plans to rezone Panmure and Glen Innes for high-density housing.
She opposed new Housing NZ blocks at Talbot Park, and has been part of a wider group that has protested against every state house removed or demolished in a huge redevelopment that envisages 7500 mostly private homes to replace Tamaki's 2800 existing state houses.
Earlier this month, she led a march up Tripoli Rd against legislation giving ministers powers to sell state houses.
"You can never think about yourself because you wouldn't cope," she explains. "That's why I've plunged myself for 30 years into helping the people with housing - because it's dangerous, it's lethal, to think of myself."
With no family roots, she has also found another way to ground herself, literally. Mr Underwood brought in topsoil for the Clairville Cres home back in the 1950s and built up a productive garden which they have expanded together.
"I never thought I'd say I'm happy to be sober, but I really am today, and having stability here has been part of that.
"It's impossible to stay sober without a permanent, stable roof over your head."
