Screenwriting 101, they say, is create conflict. Christine “Lady Bird” McPherson (Saoirse Ronan), the protagonist of writer-director Greta Gerwig’s Lady Bird, is a constant source of conflict, perennially fighting with all those around her. For what, she’s not always sure, it’s simply who she is. Her fighting is a form of self-expression, she’s fighting for her self-expression. As she says when a Father at her Catholic high school asks if “Lady Bird” is her given name- “Yes, I gave it to myself. It’s given to me, by me.” Set in 2002, Christine’s roller coaster final year of high school provides…