Jen Bridges-Chalkley took her life at her mother’s home in October 2021.
She had been referred to the children and adolescent mental health service, known as CAMHS, three times before that.
Senior coroner for Surrey, Richard Travers said at the inquest earlier this week.
“For much of the time between May 2018 and June 2020, she was on a waiting list for therapy from the psychology team and was awaiting assessment.”
He concluded CAMHS had failed “to properly to assess, diagnose and treat Jen, in order to manage her conditions and minimise her risk of suicide”.
All of the organisations concerned in her care say they will learn from the findings and make changes.