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It was the day she and then organising committee chairman Logan Evans were chatting to Prime Minister John Key and deputy Prime Minister Bill English when they were "photo-bombed" by Road Safety Southland mascot Harry the Hippo.
"That was so hilarious," Mrs Paterson recalled.
Thousands of people will converge on the small, rural settlement of Waimumu this week for the event, which is held every second year — this year from Wednesday to Friday.
From its beginnings in 1982, it has evolved into the largest event of its type in the South Island and is second only to Mystery Creek nationally.
It will be Mrs Paterson’s last field days after six and-a-half years in the position, during which time she has seen it grow from 400 exhibitors to about 750 this year.
Mrs Paterson, who farms Waikaka Station at Greenvale with her husband Laurie and son and daughter-in-law Ross and Steph, joined the field days team in August 2013 thinking — "this sounds crazy now", she laughs — that she would have have one year doing field days work and then a year off, giving her more time to spend at home.
When she started the role, the piles were being put down for the Agri Centre and, every year since then, something had been done. The most recent addition was the new toilet block, something she was particularly pleased with.
"Every time I think I’ll have a year off, my lovely committee dream up some other wonderful adventure or task."
Mrs Paterson agreed most people would not comprehend the scale of the organisation of the event "until you actually get in it".
When she started, there was one row of exhibitors in paddock four; now, that was a full paddock and paddock five had been added.
There had been "huge leaps and bounds" since 2013, including consent to allow the facility to be used for other events.
Strategic planning had been done and the event, which now had structure, had "moved into the 21st century".
But Mrs Paterson stressed the event was not just about her — it was a team effort, and she derived satisfaction from helping set up the committee to succeed.
Money raised over the years had been used to buy the 60ha site, along with building the Agri Centre and other infrastructure.
Ironically, Mrs Paterson much preferred it during the rest of the year when there was "150 acres and no tents".
By the time field days week came around, she admitted she was very tired — "you function through it ... hit auto pilot", she said.
It was an all-consuming job, although she acknowledged that could have something to do with her nature.
"Maybe I make it that, I like to do the job right," she said.
She has been helped recently by her replacement, South Otago woman Jude McNab, who was coincidentally born and raised in Waimumu.
Mrs Paterson felt she did not have the energy left to grow the event to the next step, and somebody else was needed to come in with passion and enthusiasm.
During the event, she did not have much time to get out and about around the site, but one memorable occasion was showing then National leader Bill English around, shortly after he had resigned, and "having a yarn".
She had made some "fantastic" relationships through her involvement with the field days, and it was the contact with those people she would miss.
Some contractors she knew she could "ring up now and get a tent or 40 toilets — you know these guys are going to come through".
There was no fear of boredom setting in once she finished the position at the end of the month; the Paterson family is heavily involved with Hereford cattle and the World Hereford Conference is being held in the South in early March.
Then there was the 75th jubilee of her local Maitland dog trial club and there would probably be no down-time until April.
Then an agri-tourism venture was getting under way, which included opening Paterson Park and Gardens for garden tours later in the year.
On the farm, Mrs Paterson’s particular interest was the Texel sheep stud — she is vice-chairman of the Southern Texel Group — and she was also looking forward to spending more time with her grandchildren, her horse and her dogs.