SA mum accused of daughter's sex abuse

A mother has gone on trial in Adelaide accused of twice sexually abusing her daughter when the girl was aged six.

Prosecutor Sarah Attar said the girl first revealed the abuse to her foster mother in 2012, three years after Families SA removed the child from her mother's care.

The woman, 53, has pleaded not guilty in the South Australian District Court to two counts of unlawful sexual intercourse with a person under 14, between September 2008 and March 2009.

Opening the trial on Thursday, Ms Attar told the jurors that the now 12-year-old girl was the crucial witness for the prosecution and unless they were prepared to accept her evidence beyond a reasonable doubt they must acquit the woman.

She said a social worker would give evidence about the family's home, in rural South Australia, being in a filthy state, while the girl's teacher would say she sometimes wore dirty clothes to school.

Ms Attar told the jurors the evidence would be called so they would know something about the living conditions at the time, not so they would think it showed she was the type of person who would abuse her child.

The trial is continuing before Judge Peter Brebner.