In her book, Kate gives a clear and definite reason for not answering police questions. She was following the advice of Carlos Pinto de Abreu, her lawyer
It should be mentioned that this lawyer was at the McCann's villa until 4.00 am the night before
He had accompanied Kate home after the first day of questioning, and she says, in her book, that she was horrified by his advice that she should consider confessing that Madeleine had died in the apartment and her body was hidden or disposed of
Kate goes on to say her confidence in Carlos evaporated almost as quickly as her faith in Portuguese justice, and that not being able to tell if he believed them or not was a major worry, to put it mildly
She added that she was no longer sure he had the backbone to stand up for them, and that Gerry had demanded whether or not Carlos felt he was up to the job
A few hours later she was, it appears, following his instructions without question
In the circumstances, and given Kate's obvious lack of faith in her lawyer, she might, rather, have followed the advice given by police liaison officer, Bob Small ( described by Kate as 'one of the good guys' ) the night before :
... "Just tell the truth"