So even though Stanford was founded co-ed, there was a limit on female enrollment till 1933 by Jane Stanford because she did not want it to be called the "Vassar of the west".
Between and 1933, there was a policy in place limiting female enrollment to 500 students and maintaining a ratio of three males for every one female student. By the late 1960s the "ratio" was about 2:1 for undergraduates and much more skewed at the graduate level, except in the humanities. As of 2005, undergraduate enrollment is split nearly evenly between the sexes, but male enrollees outnumber female enrollees about 2:1 at the graduate level.
After the 500 rule was lifted, the number of women on campus increased greatly, which increased demand in sororities, but the number of sororities did not change. Moreover, sororities were much stricter back then, requiring women to sign out and inform when they would be back. Behavioral issues increased and some women asked for sororities to be banned so that women could be unified.
In 1944, the board of trusties banned sororities but not fraternities. In the late 1970s, students demanded that the University allow sororities back on campus. The resurgence in sorority interest was partly due to Title IX, which was passed in 1972 and prevented inequality in education. As a result, the ban on sororities was lifted in 1977, but Sororities did not regain housing for another 20 years.
Here is the Stanford Daily article on it- http://daily.stanford.edu/article/2004/11/12/greekLifeHistoryOfFraternitiesAndSororities