When Charlie is born blonde, both her parents are surprised. Both them and their first daughter Lily have brown hair. The first few years everyone just calls her Charlotte until her uncle Charlie calls her Charlie once. After this most other people call her Charlie, excluding her parents. When Charlie is four, her nickname turns out to be correct, since her hair is slowly turning red. The only way confusion is avoided is because her parents call her Charlotte and her aunt Romy calls her husband Charles rather than Charlie.
Charlie's hair keeps getting darker but it stays mostly red.
Until she is about twelve she hates that she looks so different from her sisters but eventually she learns to appreciate her red hair and freckles. Her uncle Charlie is her absolute favourite and will stay this way even when she is an adult.
Charlie starts Hogwarts in September 2031