And as of today she has another horse to add to her own stable.
"I'd seen other trainers taking on Kaimanawa horses and admit it was something I had always wanted to do. Not only do you have the opportunity to work with a wild horse, you also get to save a life."
The Kaimanawa horse muster is held every two years. This year 170 horses were successfully re-homed following the weekend's muster from the Waiouru Military Centre.
Kaimanawa Wild Horse Preservation Society (KWHPS) placed 13 horses and Kaimanawa Heritage Horses (KHH) re-homed 157.
A month out from the muster about 60 horses had homes, but the application total eventually came in at over 270 with KHH receiving an influx of applications in March.
The re-homing applications is a record number in the history of wild horse re-homing.
Logistically the group can only re-home a maximum of 160 horses from one muster so the Department of Conservation (DOC) and KHH are planning a second operation for the last week of May 2018 to muster and re-home a further 150 horses.
At the last muster O'Brien asked for an older stallion after learning they were the hardest to re-home.
"And I got Tama – the coolest little dude ever," she said. "He must be about 14 years old and was undoubtedly a dominant horse in the Kaimanawa pack as he's covered in old battle wounds."
Tama is being trained as a pig-hunting horse. "He didn't have the skills to be a show jumper but is incredibly sure-footed in the bush."
O'Brien has also asked for an older stallion this time around.
"Kaimanawa horses are a lot of work but I have learned so much about myself in the process. The biggest requirement is patience, wild animals go at their own pace and not at a pace you think they should. Some days I spend 15 minutes with Tama and other days I'm able to work with him for a couple of hours.
"I have also learned a lot about horse psychology during the past two years."
All this will be put to the test with the arrival of O'Brien's second Kaimanawa stallion.