I highly doubt that being admitted to this university involved any kind of "contract" guaranteeing the students that the university would remain women-only, but if it did, then they may have a case.
Way back when I went to college, the college catalog of available courses that contained the curriculum for specific majors and which was in effect at the time a person declared a major, was considered a "contract" between the student and the school. Purportedly, it meant that the school could not add or change requirements to that person's future schedule for classes. Of course, the school always did, but in my experience, it was done without much hassle for the student. Others certainly might have different experiences and horror stories to tell. I suspect this "contract" might be what these girls are referring to, but I do not see how they can make this claim stick.
I once worked for an all women's college in Kentucky. It had originally been a school for orphaned young girls in the 1800s. It morphed into a two year college and then a four year school. Their nursing graduates were as sharp and as well trained as any in the country. The school began to permit male students in one of their off campus night programs (30 miles distant). This was viewed by the administration as a "revenue enhancer". I do not think the college has yet permitted males to enroll on the main campus.
Also note in the article the admission of men will not start for four years until the current class of freshman has graduaetd..