The major difference between women's and men's breaststroke is buoyancy. (See Olympic Breaststroke Techniques.) It may seem insignificant, but this slight contrast affects bodyline, breathing and timing—all essential keys for success in a breaststroke race.
Buoyancy is a factor because female swimmers have more adipose tissue (body fat) than men. This is healthy! Even women with minimal body fat are naturally higher in adipose tissue to support a fully functioning reproductive system. However, their body composition requires female swimmers to make one slight biomechanical alteration to their breaststroke technique.
During the stroke, it's essential for a female swimmer to thrust her head down forcefully with the goal of having her chest lead her hips through a streamline hole. This will optimize streamline, reduce drag, conserve energy and preserve propulsion.
Other than that, women's biomechanics should remain the same as men. The timing of the breath must coordinate with the arms and legs while maintaining the proper bodyline to minimize drag. Dr. Brent Rushall, a renowned exercise scientist from San Diego State University, has eloquently described the mechanics of the breaststroke in his book Swimming Pedagogy and a Curriculum for Stroke Development:
"[T]iming: open the arms while no other parts of the body move, press backward and raise the head to breathe, inhale as soon as the arm press is completed, and drive the head back down into the water to look at the bottom as the arms are thrust forward to a full streamlined stretch. Begin drawing the legs up as the head is thrust back into the water—not as the head is being raised."
Rushall, B. S. (2011). Swimming Pedagogy and a Curriculum for Stroke Development, 2nd edition. Spring Valley, Calif. Sports Science Associates.