Mary’s grandfather, Vic, said Emma had “struggled with mental health” for some time.
Mary said she found it difficult to identify somewhere she could go to remember her mother and said the charity was “amazing” when she first heard about it.
Legend on the Bench was founded by Michelle Hazard after the death of her son, Jay Lee Mead.
Hazard said: “What began as a simple idea has grown into something far more meaningful than I could ever have imagined. This project was created with one purpose, to save lives.”
She said the benches served as a reminder that support was available and “reaching out is a sign of strength, not weakness”.
Former Hull City striker Dean Windass, who has previously discussed his own struggles with mental health, said the charity was “unbelievable”.
Windass was among the guests at the unveiling of the bench and said Mary was an inspiration.
“She’s got through the other side and her mum would be very proud,” he added.
“The more benches we have, especially in Hull, the more lives we can save.”