The child began a series of weekly appointments on November 24, 2015 where she was encouraged to explore her emotions through verbal and visual means.
After Milly's first visit, the therapist advised Fiona Tuomey to make an appointment with the HSE's Child and Adolescent Mental Health Services.
An appointment was made for January 30, 2016, but this was brought forward after Mrs Tuomey found a "suicide diary".
"She'd written in biro on herself, 'beautiful girls don't eat'," Mrs Tuomey told Dublin Coroner's Court.
"We were terrified. We had no experience of this and no idea what to do," she said.
The family was advised to go to their local Emergency Department if any concerns arose over Christmas or out of hours.
The court heard that on November 3, 2015 Milly posted on her Instagram to hundreds of friends that she wanted to die on a certain date.
Then, on January 1, 2016, the family ate dinner together and watched a film. That evening, Milly declared that she was bored and left the room.
She was found moments later in a critical condition and emergency services were called.
She was rushed to Our Lady's Children's Hospital where she died on January 4.
Coroner Dr Myra Cullinane yesterday returned a verdict of suicide at her inquest.
Irish children as young as seven have expressed suicidal ideation, psychiatrist Dr Antoinette D'Alton told the coroner's court.
"Years ago this would have been unimaginable. Now suicidal ideation is increasing in children as young as seven. There is a care pathway but it is under- resourced," Dr D'Alton said.
Ireland currently ranks fifth in Europe in cases of suicide in the ten to 14 age group.
The past decade has seen a "step by step increase" in instances of non-fatal self-harm among the same age group, according to director of research at the National Suicide Research Foundation, Professor Ella Arensman.
Dr Cullinane commended the Tuomeys for their decision to donate their little girl's organs.
The coroner noted comments from experts who stated further resources were required for child and adolescent mental health services, and recommended the provision of information to support parents and families while they wait to be seen by services.
In a statement after the inquest, Milly's parents Fiona and Tim said they were traumatised by the tragedy.
"Milly was loving and greatly loved, fit, healthy, connected, engaged and talented," they said.
"When we discovered, out of the blue, that our child had told her friends on Instagram that she had chosen the day she would die, we couldn't believe it. We did not know what to do," they said.
The family said that they discovered there are no clinical protocols for when a child has a mental health crisis.
"In 21st-century Ireland this is simply not acceptable," they said.
They had hopes and dreams for their daughter, and Milly had hopes and dreams for herself, they said.
In an excerpt from her diary, Milly told how she hoped to be a "famous doctor", get married and have children.
"When I am 23 I would like to have my first baby and when I'm 24 my second baby. If I have two girls I want to call them Vanessa and Grace Tuomey," she wrote.
Where to get help
• Lifeline: 0800 543 354 (available 24/7)
• Suicide Crisis Helpline: 0508 828 865 (0508 TAUTOKO) (available 24/7)
• Youthline: 0800 376 633
• Kidsline: 0800 543 754 (available 24/7)
• Whatsup: 0800 942 8787 (1pm to 11pm)
• Depression helpline: 0800 111 757 (available 24/7)
If it is an emergency and you feel like you or someone else is at risk, call 111.
