Patrice Brown denied making the 12-minute clip of the police interview with one of Dwayne Kesto's victims at Wolverhampton Crown Court.
Kesto was jailed for 16 years in July for raping two girls, police said.
Brown, who said her phone recorded it automatically as it was malfunctioning after being dropped in a toilet, was convicted of contempt of court.
The court heard Brown had been in the public gallery during her boyfriend's trial but suspicions were raised on the second day about her making an illicit recording.
She was arrested two days later on 14 July.
When police checked her phone they found the video clip and audio clips discussing the trial which had been sent to Kesto's mother via WhatsApp.
The 28-year-old student, of Parkfield Avenue in Wolverhampton, denied she was "particularly interested" in the evidence of one of the complainants.
She said: "I was not there to contempt the court, I was just there to get the truth."
Tom Kenning, defending, said evidence indicated there was a "real possibility" the phone malfunctioned, or Brown "inadvertently" activated the recording.
But Judge James Burbidge said there were "too many coincidences" to suggest the phone started recording at the same moment key evidence was being played.
Brown will be sentenced in January.
The girlfriend of a paedophile rapist used her mobile phone to record one of his victims giving evidence in court.