Sophie Parkinson was found dead at her home in Liff, near Dundee, in 2014 having taken her own life.
She had been seeking help from local mental health services from the age of seven.
Ruth Moss, mother of the High School of Dundee pupil, blames NHS Tayside for her death and is privately suing the health board in parallel to the inquiry.
A hearing was held at Dundee Sheriff Court today at which lawyers for the Crown, Mrs Moss, NHS Tayside and the High School of Dundee had been expected to agree dates in January for the inquiry to take place.
Sheriff Drummond chose to set a further preliminary hearing – the third so far – for January 16, and instructed parties to agree witnesses and a timeline of events for that date.
She told the lawyers present: “I want to make sure we get a firm grip of this inquiry.”
Following the hearing, Mrs Moss said: “It has been postponed, but it has been postponed for the right reasons. This absolutely needs to be done right.
“I would like to make sure that everyone has a chance to be heard. If that takes a little bit longer – it does seem like a very long wait – hopefully we will get the answers in the end and there will be some real changes from it as well.
“That’s my hope for the end of it. I have nothing else to say.”
The full inquiry is expected to take place in the spring, over the course of at least five days.