What does shaving your head symbolize?

The symbol of a shaved head has signified devotion, rebellion, and even sometimes, a sign of a mental break. Women have shaved their heads out of convenience, to stay clean, and as an act of repentance.

Do female monks have to shave their heads?

Most Buddhist nuns and monks today follow the Vinaya rules about hair. Practices do vary somewhat from one school to another, but the monastic ordination ceremonies of all schools of Buddhism include head shaving.