William Tyrrell's foster mother hit with fresh charge

The former foster mum of William Tyrrell is facing a fresh charge unrelated to William. Photo / Supplied

William Tyrrell's foster mum is facing a fresh charge, separate to the assault of a child charge she and her estranged partner pleaded not guilty to last year.

The new charge was revealed as the boy's foster mother, 56, and foster father, 54, faced Hornsby Local Court in NSW on Tuesday for their original assault charge, to which they have pleaded not guilty.

The original charge does not pertain to William Tyrrell.

In December, representatives for the pair indicated to the court they would submit an application under Section 14 of the Mental Health Act, which allows a person charged with a criminal offence who has mental health or cognitive impairment to avoid a finding of guilt or criminal conviction.

Sharon Ramsden, who appeared for the woman on Tuesday, told the court a mental health assessment had been conducted with her client and a report would be ready in the coming weeks.

Having received the fresh charge on Friday, she said further consultation would be required with the psychologist before it could be properly addressed.

The former foster mum of William Tyrrell is facing a fresh charge unrelated to William. Photo / Supplied

She did however enter a not guilty plea on behalf of her client in connection to the new charge.

The lawyer for the foster father, Lauren MacDougall, said the Section 14 application flagged during December's court date would no longer be pursued for him.

She said it would be appropriate for the man's matter to be next heard alongside the woman's.

The fresh charge is expected to be addressed in conjunction with existing matters.

Medical material was to be filed and served for the woman by April 8, with both parties to return to court later that month.

Neither the child who police allege was assaulted nor the couple can be identified for legal reasons, while non-publication orders also restrict media reporting on the nature of the allegations.