Thomson was questioned for eight hours about her visit to Israel, who she knew, and her intentions.
She said they asked if she knew Arabic because of her Lebanon visit.
"I said there hadn't been enough time to learn it, given I was there for only three weeks.
"A couple of hours later I was summoned by a new guy who said I think something about being security and intelligence. He asked me a lot of the same questions and grilled me about who I know there.
"He demanded that I tell him about everyone I knew in Israel. It was awful knowing that I may have compromised others working for the peace organisation."
One interrogator mockingly congratulated her for winning a $500 prize for an essay she had written on Iranian politics which appeared on the Massey University website.
"I felt humiliated and ashamed. Eventually it seemed to me that he had found something out and knew that I had lied about something."
Exhausted, after a 24 hour flight and 12 hours questioning, Thomson admitted that she was to work for a non-governmental organisation.
She was transferred to a detention centre and held with other detainees for 36 hours.
Her belongings were confiscated except for an electronic book reader. She was allowed one phone call to the nearest embassy in Turkey.
She said she regretted not being honest but it was a valuable experience.
"I know what it's like for the Palestinians to deal with what they deal with every single day."
The centre said it advised interns to travel on tourist visas as they could not get volunteer visas from Israel.
Thomson said the organisation was very apologetic. They said their interns had never been detained.
Thomson was banned from Israel for 10 years.
