"Margaret didn’t go on the holidays with us. I never saw her at the house. When we went to their house we sat in the living room.
"There could have been someone else upstairs, I don’t know."
Rosemary met the carers in the late 1980s when they took over a hotel in Inverkip. They remained friends but she had no clue Margaret was even living with them.
It is believed Margaret lived with her dad in Port Glasgow before he died in 1995. She then moved in with her grandparents and mother before living with her carers in 1997.
Specialist search teams have been hunting for clues - such as clothing and documentation - that will assist them in their investigation.
A police helicopter, dog unit and dive teams have also been searching across Inverclyde.
Detective Chief Inspector Paul Livingstone stressed they were still treating the search for Margaret as a missing person investigation.
He said: "Margaret did have a private side to her life that even her carers didn't know about.
"They know she went out, they know she had friends but she kept it very much private and to an extent secretive from them.
"We know that Margaret went to James Watt College in Greenock between 1996 and 1998 and have traced several of her classmates and friends, including lecturers.
"However it could well be that Margaret had other friends from that era and we're quite keen to speak to them.
"She was described as being very quite but very pleasant. She got along and she had no disagreements or fall outs.
"She could have a double life for all we know."
He previously said he had "become very concerned for her whereabouts and wellbeing".
“One line of enquiry that I now must consider is the possibility that Margaret may have come to some harm", he warned.
The carers are not being considered as potential suspects and have been assisting with enquiries.
"They're naturally upset and concerned about Margaret, it's been over six weeks now", DCI Livingstone said.
We told how officers scoured the house and the surrounding area for Margaret.
Police have also drafted in a mobile command centre as they stepped up the search.
"We will cover every blade of grass, turn over every stone in the garden in an attempt to find even the slightest bit of information or evidence that could lead us to where Margaret is."
And DCI Livingstone also appealed for anyone at college with her 20 years ago to get in touch.
He added: “If anyone remembers Margaret from James Watt College in 1996, 1997 or 1998, whether a student or lecturer, please get in touch.
“We have spoken to a friend she met there but we are keen to find out if there is anyone else who may still be in touch with her.”
“Margaret’s carers have said that they believe she has a private side to her life and that she may have friends that they are not aware of.
"We are currently working with very limited information which makes this a challenging investigation.
“If you know or knew Margaret, please get in touch with the investigation team based at Greenock on 101. Any small piece of information may be able to assist us.”
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