The 25-year-old was killed a decade ago when a Russian missile struck a Malaysian Airlines flight over Ukraine, killing all 298 passengers and crew, including 38 Australians.
"I always feel sad but sometimes it's more in the background than in the foreground," Ms O'Brien told AAP.
"But this week it's right at the front of our minds."
Jack O'Brien was among 38 Australians killed when flight MH17 was shot down. (HANDOUT/DC5)
Jack was on the flight returning from a holiday and preparing to move out from home.
The Boeing 777 MH17 was about three hours into its 12-hour flight from Amsterdam to Kuala Lumpur when contact was lost.
"He blossomed into a really lovely, thoughtful, strong adult," Jack's mother said.
"He's always on our minds and we always mark birthdays and anniversaries, even the day when he went on his trip.
"We look back at messages he sent us or photos we got back."
Jack's mates and the local footy club installed a memorial plaque on a plinth and seat.
His family has befriended people at home and abroad who lost loved ones.
Jon, Bronwyn and Meryn O'Brien attended an inquest into the death of six NSW people, including Jack. (Dean Lewins/AAP PHOTOS)
"(There's) solidarity and understanding when you get together, you don't have to do too much small talk, you just know what the other people have been through," Ms O'Brien said.
"That's been really important."
Almost 100 family members will be at a commemorative service at Parliament House on Wednesday, along with diplomatic representatives from affected countries and Australian officials involved in the response.
"Those killed that day remain in our hearts," Foreign Minister Penny Wong said.
Dutch Ambassador Ardi Stoios-Braken echoed that holding the perpetrators to account was a priority as she expressed her sympathies to the families and underlined the "steadfast commitment of both the Netherlands and Australia to achieve truth, justice and accountability".
Ms O'Brien said she didn't have "unrealistic expectations" three people convicted in the Hague in absentia would serve their life imprisonment sentences as they remain protected by Moscow.
"Russia still denies any responsibility, which is just ridiculous and terrible," she said.
Ms O'Brien said she didn't like the word closure because "our grief will never end," but finding justice included exposing the truth.
Being able to determine the truth and Russia's involvement was an important part of the process, Australian Federal Police assistant commissioner Hilda Sirec said.
"For me, knowing what the truth is and doing everything we possibly could to put information towards a criminal court was an incredible privilege," she told AAP.
"We know the truth, that is a part of justice but I can't possibly know what the families are thinking in terms of justice."
The assistant commissioner was one of the first investigators on the scene, and it's one she'll never forget.
"I still have vivid images of that area, I remember when the first day I got into the crash site, it was quite a large, overwhelming scene, to be honest, it was more than 50sq km," she said.
Ukrainian Ambassador Vasyl Myroshnychenko commemorates the anniversary as "a day steeped in sorrow", saying it was important to keep pressure on holding "the criminals of the Kremlin" to account for the shooting and invasion of Ukraine.
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