Margaret Fleming was reported missing in October 2016, but prosecutors claim she has not been seen since December 1999.
Her carers Edward Cairney, 77,and 58-year-old Avril Jones deny murdering Miss Fleming, who was reported missing in October 2016 from the home they shared at Seacroft on Main Road in Inverkip, Renfrewshire.
Jones appeared at the High Court in Glasgow yesterday to enter a not guilty plea through her defence QC Ian Duguid.
Cairney, who is represented by QC Thomas Ross, was not in court after being excused attendance. Mr Ross said: “He has mobility problems.”
Judge Lord Matthews set the trial for 23 April at the High Court in Glasgow. Prosecutors allege the pair assaulted Miss Fleming between 18 December 1999 and 5 January 2000, when she was aged 19, by means unknown and murdered her.
The pair has been charged with abducting and murdering Miss Fleming and claiming £182,000 in benefits by fraud by pretending she was alive.
It is alleged Cairney and Jones abducted Miss Fleming at her home in Inverkip.
They are accused of locking her in a room before assaulting her, cutting her hair and bounding her arms and wrists with tape on various occasions between 1 November 1997 and 5 January 2000.
The pair is also accused of pretending to Department of Work and Pensions officials that Miss Fleming was alive between 18 December 1999 and 28 October 2016.
They are alleged to have fraudulently claimed £182,000 in benefits over this period. The pair face two charges of attempting to defeat the ends of justice by boarding a train to London on 25 October 2017.
They are accused of carrying £3,500 in cash and keys to a safe deposit box that contained £27,000 and to have pretended between 18 December 1999 and 26 October 2017, that Miss Fleming was alive.
They deny all the charges against them.
Cairney is also accused of assaulting Miss Fleming’s mother, Margaret Cruickshanks, on 26 November 1997 at Seacroft by pushing her against furniture, knocking her to the ground, placing his hands round her neck, compressing her throat, threatening her with violence and repeatedly spitting on her face.
Ms Cruickshanks had previously told a jury she last spoke to her daughter more than 20 years ago.