I wont give a full answer but I will give a few ideas to help you build your own unique story! :)
Okay, so I guessing you've read the book so you know that Katniss has a very parental protective relationship with Prim.
Also reading the book you know that the capital is very glamorous but has this secretive scary element to it that everyone likes to dismiss.
Remember, everyone in the capital is very over the top and exotic and you (Katniss) is very plan compared to everyone else being from district 12
Hope this gets your creative brain flowing :)