Claire Parker staged fights in the garage of her home
Three people have been convicted of a series of offences, following a BBC investigation into one of Europe's largest dog-fighting syndicates.
Claire Parker, 44, from Lincolnshire, Mohammed Farooq, 33, from Birmingham, and a 17-year-old boy were convicted at Lincoln Magistrates' Court.
The RSPCA said it was one of the biggest cases of dog-fighting it had prosecuted.
The convictions follow an investigation by the BBC's Panorama programme.
The charges followed the programme's probe into links between a dog-fighter and the gang in Northern Ireland who supplied US pit bull dogs and travelled to fights as far away as Finland.
Parker, a mother of three of Kexby Lane, Kexby, was found guilty of holding a fight in the garage at her home, which she shared with her husband John Parker. He has since died in prison.
She was found guilty of being present at a dog-fight, keeping a premises for dog-fighting and possessing three pit bull dogs. She denied all the charges.
Dog-fighting is a barbaric and cruel so-called sport which belongs in the Dark Ages
Chief inspector Ian Briggs, RSPCA
Mohammed Farooq, 33, of Daniels Road, Bordesley Green, Birmingham, was found guilty on two counts of causing unnecessary suffering to an animal and possessing training equipment for dog-fighting.
The 17-year-old was convicted on two counts of causing unnecessary suffering to an animal, and keeping dog-fighting equipment.
Both he and Farooq earlier admitted owning a banned pit bull.
They will be sentenced on 25 September.
Chief inspector Ian Briggs, from the RSPCA's special operations unit, said: "Dog-fighting is a barbaric and cruel so-called sport which belongs in the Dark Ages and horrific suffering is caused to the dogs involved.
"Those that continue to pursue this activity should understand that the RSPCA and the police will continue to bring those responsible before the courts."
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