John Nichols was also found guilty of the same offences because he allowed her to drive knowing she had been drinking and failed to tell her to slow down.
The judge at Nottingham Crown Court, Recorder Gregory Dickinson, QC, remanded them in custody for sentencing on November 21 but warned the two that lengthy custodial sentences were "absolutely inevitable."
The tragedy happened on May 12 last year after Butres, of St Mary's Street, Stamford, a senior executive with packing firm BM Partnership Ltd of Ely, went to Nottingham racecourse with Nichols. She and Nichols, a director with the same firm which employs 63 workers, plus 100 agency staff, later told police they drank about a bottle and a half of wine between them.
Nichols, of Manor Road, Carlby, let Butres drive them home because he had drunk most of the wine.
The court was told witnesses noticed how quickly the Jaguar was being driven. A special 'black box' in the car showed it had been travelling at 113mph – whereas other traffic had slowed to 40mph because of the standing water.
Butres claimed she had drunk two glasses of wine and had been driving at between 70 and 80mph when the car went out of control.
Gordon Aspden, defending, asked for a psychiatric report to be prepared after revealing Butres has suffered from post-traumatic stress disorder since the crash.