When Tic is telling Montrose about the differences between his son's book and real life (Christina being a man, George surviving Ardham, Dee being a boy), he is actually talking about the differences between the show and the book it's adapted from.
The soundtrack being played during a scene when a determined Dee rides away from a tense situation on her bike is from a speech by 11yo Naomi Wadler given during a March for Our Lives rally/march in Washington DC of March 2018. Wadler has campaigned tirelessly to raise awareness of the African American girls and women who have been victims of gun violence but largely ignored in the national conversation.
The baseball cap that Dee wears is for the Chicago American Giants, which was a professional team in the Negro leagues from 1910 to 1956.
Dee's friend who was killed turned out to be Emmett Till. 14 yr. old Emmett was visiting relatives in Money, MS when he was accused of whistling at Carolyn Bryant, a white woman. Four days later, Bryant's husband Roy and his half-brother J.W. Milam kidnapped Till from his great-uncle's house, beat him, and shot him in the head before wrapping his neck in barbed wire, attaching the wire to a 75-pound metal gin mill fan, and dumped the body in the Tallahatchie River.
For her son's funeral in Chicago, Mamie Till insisted that the casket containing his body be left open, because, in her words, "I wanted the world to see what they did to my baby." By 1955, African Americans across the country, including in the segregated South, had begun the struggle for equality and justice. Emmett Till's murder was a spark in the upsurge of activism and resistance that became known as the Civil Rights movement.