Antigone, as portrayed in the eponymous play by Sophocles, is certainly a strong and independent-minded female character. She refuses to compromise her belief that her brother should have a proper burial, even though she faces death as punishment for her actions. While she is a strong woman, the word "feminist" is often used as a specific term that refers to much more recent women’s liberation movements, so she probably can’t be called a feminist, per se. Her character could, however, be examined through the lens of contemporary feminist writing and criticism.
Some contemporary feminist media critics, such as Anita Sarkeesian, look closely at portrayals of female characters in video games, movies, plays, and TV shows. They ask questions such as the following:
- Are the women in this media portrayed as passive objects to whom things happen, or do they take action to influence their surroundings and affect the outcome of their situation?
- Are they idealized? That is, are they presented as having traits that cater to a male concept of perfection, or do they come across as real people?
- How do these women relate to male characters? (This would pertain to your idea of looking at how Antigone relates to her male family members.) Are they portrayed as having a role that merely props up male characters, or can they stand alone as characters in their own right, with their own histories, strengths, and flaws?
Asking these questions and others like them—you may want to look up Anita Sarkeesian, Roxane Gay, and other feminist media critics—will likely help you with structuring your thesis statement. One example of a rough thesis might be “Although Antigone is a tragic character, she is not a passive figure but rather acts to change the outcome of her life—and death.”
There are also extensive character and plot analyses on this site. Reading through these may jog your mind in terms of the character and her relationships, or might send you in another direction entirely!