A mother and daughter died in a suspected suicide pact after being targeted in a tortuous con trick by a woman who used a string of fake personas, a bogus stem-cell trial and a fictional government coverup to extort money from the pair.

Margaret McDonough, 52, and her daughter, Nicola, 23, died after they were found badly injured in a Premier Inn in Greenock, Scotland, after Linsey Cotton, posing as a lawyer, told them they faced decades in jail for breaching confidentiality laws.

The threat was part of an elaborate story concocted by Cotton, in which she used a fake identity to romance Margaret’s 33-year-old son, Michael, then pretended to be the fictional woman’s siblings, parents, nurse and lawyers to defraud him and his family.

When police searched Cotton’s home they found 15 mobile phones, two laptops and two tablets that she used to convince the McDonoughs that they were communicating with more than a dozen people. Her scam had netted her nearly £5,000 and a large number of gifts.

Cotton, 33, of Addiewell, West Lothian, was on Thursday remanded in custody at Paisley sheriff court after pleading guilty to obtaining money by fraud and threatening Margaret and Nicola McDonough before their deaths. She will be sentenced next month.

Cotton’s scam began in May 2012 when she used her stepsister’s daughter’s name and photos to create a fake profile under the name Stephanie Wilson on a dating website. Michael McDonough contacted her and they began speaking regularly, until he believed he had begun a love affair with the woman he knew as Steph. He was duped into buying her an engagement ring worth nearly £2,000.

But every time Michael tried to arrange a meeting with Steph, Cotton made up excuses to delay the rendezvous, including that she had been jailed for a breach of the peace after a fight with her – non-existent – sister’s boyfriend.

Posing as Steph’s mother, she then told Michael that the boyfriend had attacked Steph, leaving her with bleeding on the brain. Steph’s only hope, Cotton claimed, was a stem-cell treatment being trialled by a company called Biotech Scotland. She further claimed that Michael would not be able to visit Steph in hospital because of a confidentiality agreement with the company.

Cotton then claimed that a doctor in the trial had tried to kill Steph by poisoning her, and that Biotech would be paid £100m if all the patients in the trial died. She said the government was involved and that the press had been banned from reporting the case.

“Michael was led to believe Biotech were trying to kill Steph. He was told they were killing people off,” Fraser Gibson, prosecuting, told the court.

“Linsey Cotton told him the scandal was so big the government were trying to cover it up. She said he was keeping Steph alive with his support and Biotech were preventing him from seeing her, in an attempt to kill her.”

Cotton began to involve herself in the fantasy, convincing Michael that she was like a mother figure to Steph while at the same time using her alter-ego to coerce him into doing what she wanted. He was tricked into giving her nearly £5,000, a Blackberry and an iPhone, decorating her home and even, at one point, moving in with her. At the same time Cotton began telling her friends they were engaged.

Michael’s mother and sister became involved after Cotton claimed that their testimonies would be needed to bolster a case to the European court of human rights that could help to save Steph. However, she then turned on them, claiming they had breached the confidentiality of Steph’s case, that they were to blame, and that they both faced 20 years in prison.

Cotton, now posing as a lawyer, began sending Margaret and Nicola messages saying they might have to flee the country. She demanded £5,000 to make the case go away and a further £500 to arrange a fake passport for Nicola. On 7 May 2013, she went to Margaret’s home in Paisley to discuss the crisis.

Three days later, Margaret and Nicola were found dying at the Premier Inn. Margaret died soon after, while Nicola died from her injuries three days later. Their deaths are being treated as suicide.

Cotton’s fantasy began to unravel a week and-a-half later, on 22 May, when police investigating the deaths came to visit her home. They seized the phones and laptops she used to dupe the McDonoughs and she eventually admitted the scam.

She claimed to have committed the crimes because she wanted a relationship with Michael. Her lawyer, Gerry Bann, told the court his client felt “remorse and shame for the upset and anguish her deplorable conduct caused the family”.

In the UK, the Samaritans can be contacted on 08457 90 90 90. In the US, the National Suicide Prevention Hotline is 1-800-273-8255. In Australia, the crisis support service Lifeline is on 13 11 14. Hotlines in other countries can be found here.