Esther Roseman said she discovered baby Grace lifeless in the Bednest crib at their home in Haywards Heath, West Sussex, on 9 April 2015.
Her daughter's head was "hanging over the side" of the second-hand cot and she was "angled slightly upwards".
A coroner issued a safety warning about the cot last year and expressed concerns about a lack of instructions.
How safe are Bednests?
Mrs Roseman told the hearing, in Horsham, she had just had a bath when she returned to find Grace had turned "purple in colour".
She told the hearing she screamed for help from her husband, Gideon, before dialling 999.
It was "so apparent" her daughter was dead, she said.
"There was no sign, when I made the phone call I never once said 'She's passed out', I said: 'Gracie, my baby is dead'."
A coroner's report stated Grace was found with her head over the edge of the cot, and had not been able to lift it back up.
This restricted her air supply and led to her death from asphyxia, it said.
Mrs Roseman said she had not received instructions with the second-hand cot, nor straps to attach it to an adult bed.
"I didn't have those instructions, it's a shame those instructions weren't on the side of the cot," she said.
The inquest was told the cot had one side that could be lowered but the instructions stated the baby should not be left alone in this position.
"I didn't see any risk," Mrs Roseman said.
"If I had known for one moment, in the room or out of the room she was capable of what she did, there's no way I would have slept with that side half down."
Robert Norman, company secretary of Bednest, told the hearing his employer had been "completely shocked" to hear that a baby had got its head over the side.
He said the three-sided cot was designed to allow parents to provide comfort to their baby without the "dangers of co-sleeping".
He said the product was designed and tested to safety standards.
Mr Norman said the instructions stated it should have its sides up if the child was left unsupervised but said there was not a label on the product to reinforce this advice.
He said the company had since modified the cot.
At a preliminary hearing last year, coroner Penelope Schofield issued a Regulation 28 Report to Prevent Future Deaths concerning the cot.
The hearing continues.
A mother has told an inquest about the moment she found her seven-week-old daughter dead in a bedside cot.