Lynn McCurdy, 44, re-lived an evening at a 50p disco more than 27 years ago.
Later the friends walked together to a hamburger stall in Greenock town centre.
Around midnight they went their separate ways when Elaine began to walk home, refusing the offer of a lift with another friend's brother.
Lynn said her last words to Elaine were "I will see you tomorrow."
But for Lynn, Monday June 2, 1986, began with an anxious phone call from the Doyle family, asking if Elaine was with her. By 10am Lynn was being questioned by police after the naked body of 16-year-old Elaine had been found yards from her home in Greenock's Ardgowan Street.
A post-mortem concluded she'd been strangled, the High Court in Edinburgh has been told.
The two girls went to a disco at the Celtic Club in Laird Street.
Lynn said during the evening they each drank two lagers. "I wasn't falling about. I would just be happy."
She said she would be surprised if Elaine would go off with a stranger or get into a car with someone she didn't know. She was also questioned about other friends and acquaintances.
One man, known to the youngsters as 'Daft Willie' Campbell hung around the pool hall where he could be goaded into fighting with his friend Tam Paton, who also seemed to have learning difficulties.
Defence QC Donald Findlay produced a police statement in which Lynn had told officers "I wouldn't be surprised if he (Campbell) turned violent."
John Docherty, 49, now of Dunoon, denies murder and has also lodged a special defence of incrimination, claiming the culprit might be among a list of 41 names taken from files of the police investigation into the murder.
The trial continues.