My sister's 6 year-old flower girl practiced daily for her grand entrance. She had picked all the flowers from her yard to practice with, so my Mom made a "practice" basket filled with silk petals for her to work with. At the wedding rehearsal she brought her practice basket. She told the wedding coordinator not to worry, she had developed a "technique." And that she did. On the day of the wedding, she flawlessly threw each petal over her shoulder. She was delightful!
For your flower girl, consider giving her a practice basket in advance. It'll help her practice so she won't feel shy the big day. And thanks to my mom for this great tip!
Photo courtesy of Element Studios.