The 28-year-old took to the dock at Liverpool Crown Court and told how Rachel, 54, talked her into hiring her as a business advisor.
According to the Liverpool Echo, Rachel convinced X Factor star Rebecca that was an accountant, gaining access to her funds.
Rebecca told the court: "My heart and my mind are broken by her crimes. As a result of everything, I cannot trust people, and I was always a naturally shy person. I now question everybody and it limits me socially."
It's been claimed previously that Rachel – real name Anna Taylor – stole £100,000 from mum-of-three Rebecca, including money intended for a trust fund.
Rachel was sentenced to 16 months after pleading guilty to two counts of fraud. Her husband Raymond was also jailed for five months, after admitting one count of fraud.
Judge David Aubrey insisted Rachel targeted Rebecca because of her 'vulnerability', telling her: "In the court's judgement you sought to exercise unscrupulous control and influence over your victim, Rebecca Ferguson.
"You were initially a friend of hers but the court is quite satisfied that thereafter you sought to trade on her success as a songwriter and singer."