If you’d like to read works by authors admired by Harper Lee, you might enjoy:
Jane Austen’s Mansfield Park (1814)
Truman Capote’s The Grass Harp (1951)
Mark Twain’s The Adventures of Huckleberry Finn (1885)
If you’d like to read other books set in the South, you might enjoy:
Olive Ann Burns’ Cold Sassy Tree (1984)
Zora Neale Hurston’s Their Eyes Were Watching God (1937)
Carson McCullers’ The Heart is a Lonely Hunter (1940)
If you’d like to read other coming-of-age novels, you might enjoy:
Louisa May Alcott’s Little Women (1868)
John Knowles’ A Separate Peace (1959)