"She will be great," director Stephen Frears, who directed the political drama "The Deal" about Britain Prime Minister Tony Blair, told the BBC.
Producer Christine Langan said the working title of the project, "The Queen," focuses on the week following the princess' death and how it affected the queen, Britain and the people.
"It looks at a moment in British history that was phenomenal," she said. "It is a snapshot of the country. It joins the dots of what went on that week."
Diana will not be cast, according to Langan.