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.
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.
Well, it could be centered around the concept of the American dream in relation to a girl's happiness. Maybe she overcomes obstacles in her life in the USA, like family issues, social pressure, or financial problems, and finally realizes what makes her truly happy. So, the theme might be about resilience and the journey towards happiness.
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.