Although you've phrased your question as if you're asking an opinion, evidence in the story is strong that Mason intends for the reader to see Norma Jean as a woman who seeks her independence. She has just told Leroy that she is leaving him. Despite her standing on the bluff over the river, she is unlikely to jump, as some of my students occasionally suggest, because she has worked too hard to get this far. Think about her efforts to improve and strengthen herself, both intellectually and physically. Why would she give up now?
I've provided a link to an excellent essay that examines the bird imagery in the story. Norma Jean is eager to "fly away" from Leroy, who has come home to roost because of his injury. The essay points out important passages in the story to support her desire for independence. She intends to leave Leroy and live her own life.