There doesn't seem to be any one antagonist in Jane Eyre. Jane comes across many over the course of the book, beginning with Jane's aunt and her cousin John. John torments Jane throughout her childhood, and her aunt does nothing to stop him from hurting Jane. Instead, Jane's aunt locks her in "The Red Room" where Jane believes she is attacked by supernatural forces.
Jane is shipped off to Lowood School, where she is further abused by the teachers and caretakers there. As she enters adulthood, she has already had her share of abuse and punishment by many of the people in her life. However, these obstacles make her stronger and she is able to prove her worth as an individual as an adult.