She remembers the stench, the filth, the sleeplessness, the fear. Most of all, she remembers being stripped of her power, her identity and becoming a number.

A voluntary stint in an American jail may have helped Monalisa Johnson better understand her incarcerated daughter. But she fears for her more.

Johnson is one of the second crop of participants in grim reality show 60 Days, In which volunteers go undercover in America's Clark County Jail as inmates. Their back stories must stay watertight, because discovery by their fellow inmates could easily kill them.

Not even the prison wardens know them as anything other than first-time inmates.

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The show is recorded through jail security cameras, and via a TV crew making a "mock documentary".

The biggest protection volunteers have is alert producers and a safe word that will bring help as soon as possible if it's uttered.

Monalisa's daughter, Sierra, is serving 10 years in jail without parole after being arrested for armed robbery in 2012.

Johnson has struggled to relate to her daughter since her fall from college honours student to inmate, not least because she found it hard to believe the prison horror stories her daughter was telling her.

Now, she knows even if she had believed those stories, nothing could have prepared her for the reality of prison.

"I needed to know what it was like on the other side of those walls," Johnson says.

"Now I understand her better, but fear for her more.

"My biggest fear with Sierra was always that the prison system would fail my daughter and she would come out a 'true criminal'.

"Nothing in my experience in prison has changed that. What it did more than anything was solidify that thought process."

Johnson doesn't shy away from the fact Sierra broke the law, but says the sentence she received was too harsh for a first-time offender.

"People ask me 'wasn't she a true criminal when she committed the crime?'," the frank 49-year-old says.

"The answer is yes, but she was not I consider to be a true criminal, a repeat offender, in and out of jail.

"She was what I consider to be a person who was young, dumb and hung out with the wrong crowd and made an awful mistake and bad decisions.

"We hope these punishments rehabilitate the people in jail. And what I could see with my own two eyes was it's not doing that in any way, shape or form.

"So I wonder if you're not going to be rehabilitated, what are you going to become?"

Terrified "hell yes, petrified" at the thought of going behind bars, Johnson quickly found it was worse than she imagined.

"I thought 'how could you possibly keep me safe in there?', despite the fact that we had [safe] words.

"It's eerie the moment you walk in the door.

"You realise you are no longer free and you no longer have an identity. You are a number. You have no rights at that point that you know of - unless you are smart and you have been there before."

She sat amid filth and grime, so sleep-deprived she didn't know "which way was up", swallowing down the horror.

"You feel unprotected. It's almost eerie, sitting next to a woman that you know is detoxing and is shaking because they're coming off heroin right in front of you. You're sitting next to a potential murderer."

The worst moment was having a gun pointed in her face.

"I'm laying in a bunk half asleep with earplugs in my ears and I see what I thought was an actual gun, but what turned out to be a pellet gun, pointed in my face with someone [a guard] screaming at me to 'get up and get out'," she recalls.

"The bunk was being shaken down and checked for drugs. It scared the s*** out of me. I felt like my heart was about to jump out of my chest."

"The only thing that got me somewhat prepared was listening to my daughter's stories. I wanted to believe they weren't true, but if they were true, I thought I would be prepared.

"But there's nothing that can prepare you for being treated like an animal. For being thrown into an area where you never get to come out and see daylight for 60 days."

Johnson left jail with a staph infection, an extra 5kg in weight and new appreciation of food and freedom.

To be able to eat a slice of pizza, to do whatever she wants to do when she wants to do it, sleep, sunshine and shared stories with her daughter: these are things she savours.