After a serious rupture in her achilles tendon while training for the IronMaori the mother of two needed to find a new way to maintain her love of fitness.
"Its definitely a challenge but so rewarding," she said.
O'Brien admits she hates the diet which mainly consists of broccoli, chicken and egg whites.
She drew strength from her coaches during the times she doubted herself.
"I would never have made it on stage without Greg [Bigg] and Cheryl [Summers]."
The husband-and-wife coaching team would constantly push O'Brien to new limits.
"Believe in the process," Bigg would tell her.
The Napier massage therapist said her drive came from her stubbornness.
"I've always been pretty self-driven. When I set my mind to something it's hard to stop me."
O'Brien was initially daunted by the prospect of posing on stage.
"I've never been a bikini wearer. I have the mummy tummy."
The three-hour wait didn't help the nerves.
"Everything was shaking, even my false eyelashes."
O'Brien's trademark pose is her bicep pose as she believes her arms are her best asset.
"I've struggled with my legs and find myself getting quite frustrated at times."
She said she had a love-hate relationship with the Napier stairs.
O'Brien will enjoy a bit of downtime in summer before getting back into fulltime training in the New Year.
Her dedication to her discipline hasn't been lost on her family.
The previously "extremely unfit" family members are now gym junkies and her husband has shed 15kg in recent months.
"It has definitely filtered through to my family which has been so cool to see." O'Brien wants to qualify for nationals now she has competed on stage and "not made a dick" of herself.
