Once in the country, however, immigration officials at the Queenstown Airport noted the Johnstons were paying Ms Pache's travel and accommodation, and Ms Pache admitted during an interview she would undertake childminding, although she also maintained she would not be paid.
"They asked me are you going to work here and I said 'No, I'm not, I am going on holidays but if maybe one night they want to go for a couples dinner to have a little time together, I am happy to stay with the girls'," she said.
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• Au pair wins apology over jailing
The teen was taken into an interrogation room for questioning during which she maintained she would not be working for the family while in New Zealand.
"I didn't understand what was going on and I would never have thought this would happen. For me I was not going to work so I didn't need a working holiday visa. [The immigration officer] said to me 'I can't believe they paid for all this and you are not going to work for them'.
"In the end I was crying and asking but why and I didn't understand. [Then] he said you are going to sleep at the police station because we cannot hold you in the airport for the night."
I asked them why they were punishing me
Escorted by a police officer, Ms Pache was taken to the local police station where her belongings, including her cellphone and any items she had on her person, were confiscated.
She was then shown her room for the night - a cold, dark little room filled with only a small bed, without bedding, and toilet.
"It was terrible. I asked them why they were punishing me because I didn't do anything wrong. I said I didn't want to sleep there but they told me I had no choice.
"I asked for a blanket and a pillow.. because it was freezing cold.. and they said sorry we don't have that here. [Eventually] they gave me a blanket and it was dirty and smelly and they didn't have any pillow.
"I didn't eat since the day before because I didn't have time because of the flights and everything so I asked [an officer] for some dinner and they came out with a piece of bread and an apple."
Ms Pache was permitted to call the Johnstons and inform them of her whereabouts.
"[Mrs Johnston] didn't know I was in the police cell, nobody called her. Pip was so angry. Then I asked to call the French embassy and one of the police officers said it wouldn't be worth it because it would be closed."
The next morning at midday the teen was taken back to the airport where she was put on a flight back to Australia.
She said she was given no reassurances that she would be sent back to the Gold Coast where she had arrived from and was instead told it would be her problem to find her way back to where she was staying if she was sent elsewhere.
"I told them I didn't have the money to fly [back to the Gold Coast] I can't afford it and I said you have to send me back where I came from, I don't know anyone in Australia, I don't have any family, what am I going to do?
"Then I got lucky because the guy that was going to print my ticket was actually a French guy from my high school and ... he helped me and found me a flight to the Gold Coast."
Once back in Australia, Ms Pache said she felt depressed because of how she had been treated.
"I was feeling very bad and so I needed a long week to recovery. I was alone in this huge country and nobody could help me, I didn't have my family and it was really bad. I hope this is not going to happen to other girls," she said. "They treated me like a criminal."
Ms Pache, who returned to her hometown in France last month, has since received a letter of apology from Immigration New Zealand national manager for border compliance, risk and intelligence services, Senta Jehle.
In it, Ms Jehle said the decision to refuse Ms Pache entry because she intended to work for the family was correct.
But having personally reviewed the case, Ms Jehle said, "while the decision was correct and followed Immigration NZ instructions, the consequences for you [of the decision] ... were not proportionate".
"Please accept my apologies on behalf of Immigration NZ for the stress and inconvenience this has caused you and the Johnston family."
Ms Pache said she was happy to receive an apology but hoped changes would be made within the organisation to ensure the same situation would not happen to others travelling to New Zealand.
