In this case I disagree with you. A questionable arrest and overstaying the visa in Malaysia with result in her being denied a UK visit visa. The UK will have no way of checking any Malaysian database even if it is kept up to date. She has nothing to lose by getting a new passport and not declaring the convictions, no one will know. By the way I am not naive about UK visa applications. I have successfully carried out 3 x 1 year applications, a 5 year and a 10 year visa for my Thai wife.