Two quick additions;
1) I don't know much about the fraternities, but D did join a sorority and really likes it. She is NOT your typical sorority girl, but she said there are houses that suit virtually every personality and she also says that NU Greek life is NOTHING like the wild party scene that's portrayed in the movies. We happened to be at Second City one night when the house included a large group of NU sorority girls, and in spite of my anti-sorority bias I found them to be among the nicest, best behaved, most genuine and yes, most beautiful, group of women I've even shared a theatre with. ;-D
2) Another unexpected social benefit at NU is that since Chicago is such an awesome city and is so centrally located, D has had LOTS of friends from other schools (as far away as NYC) come to visit her at NU throughout the school year. Plus since it's a huge airline hub, cheap fares make it easier for us to visit than we'd imagined.