Joyce, you need to look at the screen as a completely different medium. Summarise what your story is about, and then rewrite it for a visual medium rather than trying to adapt it. So you need to think about what elements of the story are the most important you need to get across, and how do you best present this in the time limit you have and visually.
I see so many adaptations where precious screen time is wasted on some of the irrelevant set ups in the beginning of the book because the screenwriter was too afraid to leave something out - then the second half of the movie rushes through a lot of important stuff because there is no longer time for it. You almost want to write the screenplay in the opposite direction - important stuff first, then filler if there is time for it.
All the best to both of you
