An ACT Supreme Court jury found Sarah Thomson, 34, guilty in March last year of three counts of committing an act of indecency in front of a child.

Thomson had her young neighbour, then aged eight and nine, take pictures of her in sexual poses on three occasions in 2008.

Thomson would then send the images to a man she was romantically linked to in Queensland.

Justice Richard Refshauge, in May of that year, sentenced Thomson to three years jail, to be fully suspended upon entering a four-year good-behaviour order.

Thomson appealed the verdict, with her lawyers arguing all three had been unsafe and unsatisfactory because the complainant had been demonstrably unreliable.

Thomson's legal team argued that there had been significant conflicts between the accounts given by the complainant and the evidence, including metadata contradicting the child's recollection of the sequence in which she took the images.

But prosecutors launched a cross-appeal on sentence, arguing the suspended jail term had been manifestly inadequate, the judge had proceeded on the basis of the wrong maximum sentence, and had taken into account an irrelevant consideration.

The three appeals judges were split on their decision, handed down on Wednesday.

Chief Justice Helen Murrell and Justice Iain Ross threw out the appeal on two charges, but found a third could not be substantiated.

The judges also upheld the prosecution appeal and ordered Thomson be resentenced.

While the dissenting judge, Justice John Burns, recommended the verdicts be set aside and Thomson be found not guilty.

The majority decision means Thomson will now be resentenced on two counts.

"Given the complainant's admitted uncertainty about [details of the offending] on the third occasion and the lack of any independent evidence on this matter, such as images, in our view it was not open to a reasonable jury to find that Count 3 was established beyond reasonable doubt," the two judges wrote.

The judges found Justice Refshauge had determined the sentence with reference to a maximum sentence of seven years' jail, when the maximum penalty had actually been 12 years.

"Consequently, it is very likely that the error in relation to the maximum available penalty had a significant effect on the sentences that were imposed.

"It is not clear that his Honour took her embarrassment into account (at least to any significant extent) when deciding to suspend the sentences."

Justice Burns wrote that he would set aside the verdicts on the ground they had been "unsafe or unsatisfactory".

He recommended findings of not guilty be substituted.

"The evidence of the complainant displayed discrepancies and inadequacies which lead me to conclude that there is a significant possibility that the appellant is innocent.

"Most disturbing, to my mind, was the tendency demonstrated by the complainant to convince herself, based on her exposure to the photographs at the briefing conference, of her involvement in events in which she had previously disavowed any involvement."

Thomson is expected to be resentenced in November.