Ms Hayes said: “It has been devastating to listen to how, when she needed specialist healthcare, for the first time in her life, she was so badly let down.
“She was let down at the Queen’s Medical Centre in Nottingham, who wrongly decided there was no underlying physical cause of her psychosis, and failed to carry out appropriate testing.
“I believe they simply dismissed her and looked to pass her onto mental health services as quickly as possible, which led to her transfer to the Becton Centre.
“Her mental health spiralled deeper out of control there, as she was not being treated for her condition, and the many failings and lack of care meant sadly she wasn’t properly protected from harming herself.
“My beautiful little girl has lost her life and I will never forgive the Queen’s Medical Centre or the Becton Centre for failing her.”
She added: “I have never believed for a moment that Mia ever wanted to take her own life.
“She was always a happy, healthy child and had so much to live for.”
A spokesperson for Sheffield Children’s NHS Foundation Trust said: “The inquest has been important to understand fully the circumstances surrounding Mia’s death.
“We will now carefully reflect on the evidence heard and the coroner’s conclusions to ensure we continue to provide safe and compassionate care.”