Rieck, 83, has been living with grief since the death of the "vibrant, compassionate and generous soul" in February 2021, the Brisbane District Court was told on Monday.
Rieck had been in a loving relationship with the woman for 16 years.
After selling her townhouse the woman was in the process of moving in with him, filling her car full of household times before tragedy struck.
She had asked Rieck for assistance after reversing her vehicle into a sign post, the court heard.
When Rieck got behind the wheel, he was cramped but unable to move the driver's seat after it was moved forward and household items were wedged behind it.
His sandal then got stuck under the brake pedal and he reversed backwards into a garden bed and fence.
Panicking, Rieck changed gears into drive with his foot still on the accelerator and ran over his partner before crashing into a wall.
"This is a case of ... poor judgement in that state of panic," crown prosecutor David Nardone said.
Rieck called triple zero and received instructions to perform first aid but his partner passed away.
"No punishment that Your Honour will impose upon him today will punish him more than he has punished himself on a daily basis," defence barrister Tony Kimmins said.
"He is horrifically remorseful in relation to the fact that he killed the person that he loved and realises nothing he will say ... will bring her back."
He said Rieck had voluntarily handed in his driver's licence in June 2021 and his only mode of transport was a mobility scooter at the retirement village where he lives alone.
"He lives a solitary life now," Mr Kimmins said.
The woman's son provided a victim impact statement that spoke of his devastating loss, saying her death's circumstances "still brings him to tears".
"His victim impact statement is measured perhaps because he realises that she was all those things to you," Judge Vicki Loury said to Rieck of the son's glowing description of his mother.
Judge Loury said the death was a result of a "combination of the shoes you were wearing and the fact that you drove the car when you could barely fit behind the steering wheel".
Rieck pleaded guilty to one count of dangerous operation of a motor vehicle causing death.
He was sentenced to 18 months in prison, suspended for 18 months, and his licence was permanently disqualified.
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