Sharon Rooney thought her agent was joking when she told her Greta Gerwig wanted her for ‘Barbie’. The ‘My Mad Fat Diary’ star, 35, was obsessed with the Mattel doll growing up, noting “I had Barbie everything”, and landed a small role as Lawyer Barbie alongside Margot Robbie (Barbie) and Ryan Gosling (Ken) in director’s 2023 blockbuster. But when she heard the ‘Lady Bird’ filmmaker wanted her to appear in her film, she didn’t quite believe it and had to double check her agent wasn’t playing a prank. She told The i newspaper: “My agent said: ‘I was just phoning to see if you fancied making a f…