Police are investigating the theft, which occurred in Richmond some time between 7pm on Friday and midday Saturday.
The ashes were stored inside a small blue container placed inside a white box in Grace Daley’s red Mazda 3 sedan.
“I was quite inconsolable yesterday and quite emotionally drained – feeling like I’ve let mum down a little bit too, with being the one holding on to the ashes,” Ms Daley told 9News.
“Then having to ring family and tell them, particularly my brother and my dad, that the ashes were gone, and the photos of mum were gone in the car. That was particularly difficult.”
Ms Daley’s mother died of breast cancer at the start of Melbourne’s coronavirus lockdown so didn’t get a proper funeral.
The family were waiting to give her a memorial service and release the ashes as a final show of respect.
“She wanted them to be spread in the Black Spur behind Hillsville of the mountains. I really want these ashes back so I can do that for mum,” Ms Daley said.
In a Facebook post to a Richmond neighbourhood page, she described being “absolutely distraught” over the lose.
“If you took them (or know who did), I don’t care about miscellaneous things. Keep them!” she wrote.
“But please return my mum’s ashes and photos, I’m begging you.”