You might say the title—Red Scarf Girl—tells us all we need to know about Ji-li. For starters, she has a red scarf that helps define her (head on over to "Symbols" for more on this). Early on, Ji-li explains why she wears the red scarf around:
With my red scarf, the emblem of the Young Pioneers, tied around my neck, and my heart bursting with joy, I achieved and grew every day until that fateful year, 1966. (P.5)
The red scarf shows the pride Ji-li feels about being part of the revolution and her desire to honor her ancestors who fought before her. Her sense of self leans on the scarf and what it represents to her—Ji-li defines herself by her participation in the Communist Party (via the Young Pioneers) and allegiance to revolution. Or, she does when the book opens. Before too long, Ji-li finds she's confused about the political messages Mao is preaching—she wants to support them and be part of the revolution, but she also knows some of his ideas aren't exactly fair.
The title hints at the fact that Ji-li starts out as a girl who is proud to wear her red scarf, but she changes over the course of the book. By the end, Ji-li isn't as much of a red scarf girl as when the book starts.