What should be the three challenges in my story?

Okay, so I'm writing a story for my Language Arts class! Well my story is about a girl named Rachel, both of her parents died out at sea because there was a furious storm while they were out sailing. Now Rachel & her younger brother live out on their island with their grandpa, Jay (who is also her mentor.) Her Grandpa has taught her how to sail just like how he taught her mother, and she's really good at it. Her sidekick is a dolphin named Flipper. The trial involving an overwhemling obstacle is that her brother wants to learn to sail but he is impatient and hardheaded so he goes out at sea, yet does he know a very bad storm is coming. Rachel has to go and save him! Can you guys help me with the challenges?