Claire Dyer moved to a specialist unit in Brighton because staff in Swansea could not cope with her behaviour.
Her family said a suitable facility might have been found in Wales if more research was done.
The High Court in Cardiff is hearing the review.
The 21-year-old's family obtained an injunction to block the move last year but Abertawe Bro Morgannwg University Health Board's decision to move her 230 miles (370km) was later upheld by a judge.
Ian Wise QC, representing the family, told the court Miss Dyer had moderate to severe learning difficulties and autism spectrum disorder, which results in very challenging behaviour.
He said she had been sectioned under the Mental Health Act several times in Wales and the move to Brighton was "devastating" to her.
Part of the problem was that information on the number of women with autism placed in health authority medium secure accommodation was not collected in an "understandable way", he argued.
He said it was a "failure by the relevant authorities to realise their statutory obligations".
"Our case is not that the Welsh government has or should have a policy that all patients's needs should be met in Wales regardless of the costs, neither is it the case that failure to complete all reports must have led to a breach, neither is it the case that there is a a requirement on bodies to consider all conceivable information," he said.
Judge Mr Hickinbottom responded: "You are saying that the relevant decision makers have not properly informed themselves of the relevant data and consequently could not make a lawful decision, but if they had gathered that data and made a lawful decision then the facilities might have been available, the accommodation might have been different."
The hearing continues.
The family of a woman with autism who had to be cared for in England because there was no suitable facility in Wales has launched a judicial review against the Welsh government.