Widow Annette Russill, who admitted forgery in a £1.8 million will scam, told a jury: "I cannot read or write."
Russill, 65, said she traced the signature of Southend heiress Annie Kay, then practised the signature every spare moment.
She used the signature when she disguised herself as 83-year-old Miss Kay to trick solicitors into changing her will.
Russill and daughter, Annette Spillman, 46, of Guildford Road, Southend, have admitted conspiracy to defraud beneficiaries of the wealthy spinster's estate.
Spillman's 44-year-old estranged husband David, of St Andrew's Road, Shoebury, pleads not guilty at Basildon Crown Court.
He claimed he knew nothing about the plot, but Russill insisted it was David Spillman who taught her how to copy Miss Kay's signature until it was perfected.
She said he bullied her into getting it right, even though she was illiterate.
Russill, of Leicester Avenue, Rochford, was giving evidence for the Crown on the third day of Spillman's trial.
She admitted having previous convictions for handling a stolen driving licence and theft offences, dating back to 1953, although she said she could not remember her criminal past.
However, Russill told the jury "Don't think I'm a criminal. It is not my fault I cannot read or write.
"I am not a bad person."
The jury also heard the trio cashed in on Miss Kay's fortune only hours after the heiress died at Annette's home in Guildford Road, Southend, in March 1997.
Miss Kay had moved there because she was too ill to live at her modest semi-detached bungalow in Dawlish Drive, Leigh.
The trio got together and allegedly took forged, pre-dated cheques worth more than £15,000 to a bank and a building society and drew £10,000.
Russill maintains she played no part in forging Miss Kay's signature on the cheques. It was David Spillman's work, she claims.
His trial continues.
Converted for the new archive on 19 November 2001. Some images and formatting may have been lost in the conversion.
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