Lisa Roussos, 53, made the plea as the public inquiry into the 22 May 2017 attack that killed 22 people reviews the circumstances of the death of her eight-year-old daughter Saffie-Rose.
The young victim's father Andrew Roussos condemned the response of the security and emergency services before the inquiry, saying the response on the night was “shameful”.
Saffie-Rose died after suffering massive blood loss from shrapnel wounds to her legs, caused by the explosion in the City Room foyer of Manchester Arena after an Ariana Grande concert.
She was carried outsite on advertising board by an off-duty nurse and some police officers, one of whom flagged down a passing ambulance.
A paramedic said that when inside she asked: “Am I going to die?”
She finally arrived at Royal Manchester Children's Hospital more than 50 minutes after the explosion, and was pronounced dead shortly after.
Ms Roussos was with Saffie-Rose at the concert. She was herself seriously injured and spent months in hospital.
At the inquiry, she said thanked those who tried to help Saffie-Rose and said the inquiry was not about the jobs or reputation of the MI5 and emergency services.
She said: “We understand the sheer panic and fear you were faced with that night, but until you admit the failings how can there be a positive change?”
The inquiry has heard only three paramedics ever entered the City Room on the night, and one of them briefly leaned over Saffie-Rose before moving on.
MI5 witnesses have given evidence in closed sessions at the inquiry, but a parliamentary committee found in 2018 that MI5 and counter-terrorism missed a number of potential opportunities to prevent the attack in their handling of bomber Salman Abedi's case.
Mr Roussos, told the inquiry: “The response of the security services on this atrocity should go down in history as one of the worst failures from start to finish, and that is what we should learn from this.”
He said the family was enduring a “living nightmare”, adding: “The response on that night was shameful and inadequate.
”Everyone in that City Room was let down and the people who excuse it should feel ashamed.
“What Saffie went through I will never forgive.
”That poor little girl hung in for someone to come and help her. What she received was a bloodied advertising board and untrained people doing the best they could.“
This week the inquiry is looking into the circumstances of the death of Saffie-Rose, with experts in disagreement over whether she could have survived her injuries.
Additional reporting by PA
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