They made a few forays into ocean fishing but Olive suffered from seasickness so they turned their attention to the Rotorua lakes.
Out of curiosity, Armistead looked up the International Sport Fishing Association world line class records for rainbow trout and saw opportunities, particularly in the open women's category.
Olive started strategically targeting rainbow trout using line weights where women's records were within reach.
After a few fruitless days in her dad's 3.7m (12ft) tinny going after the 2kg record, they struck it lucky on Lake Rotorua on July 17, with Olive reeling in a 1.23kg fish.
Olive said it took her about 10 minutes to reel it in and it was "really hard" but also "amazing " to land it.
They weighed it in at the Tauranga Sport Fishing Club and sent in detailed paperwork on the catch.
After months of waiting and checking the records online daily, Olive's record was confirmed in November.
Armistead said Olive - usually "quite shy" - was so excited and proud that she took her certificate to show her classmates at Papamoa Primary School the next day.
Fishing club manager Roly Bagshaw said the record was a "wonderful accomplishment".
Olive's next big catch was on October 7 on Lake Rotoiti during the Tauranga club's opening season week tournament: a world record contending 3.1kg rainbow on a 3kg line.
She landed her third potential record fish on Lake Rotoiti on December 16 - a 750g rainbow on a 1kg line.
"The 1kg line is not very strong and she lost a few. She learned a lot of angling skill, a bit more finesse - not just trying to wind it in as fast as she could."
Armistead said he felt "lucky" to have a daughter who shared his interest.
Olive said her favourite thing about fishing was spending time with her dad - "and getting a butter chicken pie at Okere Falls for lunch".