The boy, who cannot be named for legal reasons, waited for the victim to enter the shop as he watched her from a nearby car park.
He then followed her inside and stabbed her multiple times in a prolonged attack.
Det Supt Ian Fletcher said of CCTV of the attack: “Anyone who sees footage would say she is very lucky to not have very serious, if not fatal injuries.”
He likened the attack to the award-winning TV drama Adolescence, in which a teenager fatally stabs his female classmate.
The mother added: “If you’re big enough to commit an adult crime, you should have the punishment, regardless of your age. It was not a petty crime – it wasn’t petty theft.”
She told the that the family remained “scared” after the boy’s “evil and sick” attack.
She added that his age should not have spared him from a youth detention centre.
“I feel angry. We’re incredibly let down; we feel like everyone’s failed us,” she said.
“It’s disgusting. It’s absolutely disgraceful after watching [footage of the attack] that someone can say the guidelines are ‘first offence and the injuries weren’t life-threatening’.
“They weren’t life-threatening because she managed to defend herself.
“I want some justice for my child – I want some protection.”