Victoria Gayle, 32, pleaded guilty in December to preventing the lawful and decent burial of a child born in 2004.
Illness was blamed for her failure to appear at Kingston Crown Court. Sentencing was adjourned to 17 March.
Police officers involved in the case believe they saw Gayle nearby just before the hearing, the court heard.
Edward Brown QC, prosecuting, told the court that two detectives saw a vehicle being driven in an "erratic manner" and "they are convinced they saw the defendant driving the car".
Mr Brown said Gayle had proved unreliable in the past and was "a determined liar during the investigation".
He added "it seems to fit the past behaviour of the defendant".
Kate O'Raghallaigh, defending, said she was unsure whether Gayle was even able to drive.
She said her client was unwell and travelling to a hospital in Milton Keynes.
Judge Susan Tapping asked that documents be sent to prove that Gayle attended hospital, but that "she should be arrested if this is a device to avoid coming to court".
The court later confirmed it had been sent a document showing that she had attended a medical facility as a walk-in patient.
A mother who admitted covering up the death of her child for more than a decade has failed to appear at court for sentencing.