There was a formal at the end of every program (at the end of the regular program dates so both regular and advantage interns can attend).
However I believe this has been changed and now they close down one of the waterparks and have an evening party for the interns there instead. I did the Spring Advantage 2011 and we had a "Villians in Vogue" formal at CSR ballroom with dinner, desserts, music, and villain meet and greets.
However, my roommate completed a Spring 12 program and they had the waterpark party. From Jess' (disneyfreak508) trip report it looks like they had a waterpark party this semester also.
Advice: they do NOT give all interns the day off for this! So if your daughter wants to attend she should keep her ear to the ground for rumors of the party date so she can ask off in advance. We were lucky to have already asked off for a "roommate weekend trip" but when we found out that was also the night of formal we went to that for sure! It was a blast with some of the rare-ish meet and greets (Cruella, Hades, Maleficent, Evil Queen, Sorcerer Mickey, and more)! Plus all my friends and I were over 21 so we were able to hang out at the bar for a little bit also which was definitely fun.