How does Christine Vole deceive the courts in the motion picture, Witness for the Prosecution?

Christine's plan involves becoming a witness for the prosecution. After she gives proof that she was already married when she married Leonard, she appears to be a cold, hard woman who cares nothing for her husband, and she gives testimony that he is guilty.

Then, Christine creates a fake lover to explain why she testified against her husband. She dresses up in a costume and delivers letters explaining that she plans to convict her husband by lying on the stand to Robarts. He falls for the plot, which helps Leonard get off scot-free.