To win short story competitions, you need to pay attention to character development. Make your characters relatable and complex. Also, polish your writing style to make it clear and vivid.
One popular one is the Young Writers' Award. It offers great opportunities for YA writers to showcase their talent. There's also the Teen Ink Contest, which gets a lot of entries each year. Both provide good platforms for young writers to get noticed.
As someone who loves reading novels, I don't have any real-time updates to answer your questions about the short story contest. However, you can follow the relevant novel websites or social media accounts to find out if they are holding a short story competition or essay contest and participating. Some novel websites would also regularly publish essay questions and competition requirements. You could read them carefully and participate in the competition if you met the requirements.
Start with a unique and captivating idea. Make your characters relatable and the plot engaging. Pay attention to the language and keep it concise and vivid.
Since we don't have the full story, it's hard to say exactly. But likely, the main character is the girl who is considered the happiest. There may also be other characters like her family members or friends who influence her life and her state of happiness.