Good: "I saw that your philanthropy is Special Olympics. I've helped with SO events before, I really enjoyed it - do you do a lot of activities with the local SO organization?"
Bad: "I read your core values on your website and they are so similar to how I live my own life. My favorite core value is integrity...I live this every day by {insert long winded example here}."
Echoing everyone who says if there are other sororities holding informal events, attend those as well. This sorority may look great from a distance/on paper, but actually interacting with the women might be another story. In other words:
Don't do this.