Those are great questions, I'm not too familiar with single sex colleges, so I did a little light reading.

In 1982, the U.S. Supreme Court struck down an all-female admissions policy at a state-run nursing school. Fourteen years later in United States v. Virginia the Supreme Court again found the State’s interest in a single-sex admissions policy insufficient and struck down the Virginia Military Institute’s all-male policy. Yet Justice Ginsburg made sure to carve out an exception for private single-sex institutions. Currently private status is the key to existence for all single-sex colleges, and no challenges have yet been brought against a private institution’s single-sex admissions policy.

Interestingly, although only two percent of American female college graduates attended a women’s college, more than twenty percent of women in Congress and thirty percent of rising female business leaders in 2012 were graduates of women’s colleges.