Okay, this is basically letters to Prim from Katniss' daughter, after Mockingjay. Her name is Primrose Rue, and her brother's name is Cinna James. One day she finds out about her aunt, and she writes a letter. Later on, her little life comes tumbling down as she finds out more and more about her mother's childhood and what happened to her aunt.

Dear Auntie,

Mama screams for you a lot. I'll never know why.
She says you're gone, but that she'll see you again someday.
Do you know what that means?
It's too confusing for a little five-year-old girl to understand.
Mama scares my brother when she wakes up screaming. It's so hard some days.
Some days even daddy can't help her, and Cinna and I curl up in one bed so I can protect him.
Daddy sometimes wakes up, angry and evil-looking. When this happens, mama makes us hide in the bedroom and lock the door, both of us under a really thick blanket.
I don't know what's wrong. Can you help me figure it out?
It's scaring us. Mama talks of making us go live with another guy, off in District 2. Daddy yells at her whenever she says that.
Mama says it would be better for us.
I don't know what to think about it all.
Love, Prim.