Because your chapter is only a few years old is precisely the reason you should be looking to your advisers for assistance. And I think the risk management chair drinking while underage is a huge issue, since although it DOES happen, it can be cause for having your charter pulled if it was compounded with other issues, like low membership because you're the house with the bad attitude and STD's.

Now is the time for these girls to learn their actions have consequences for a whole group of women, not just themselves. And I'm wondering if there are some self-esteem issues at play here. That probably also needs to be addressed, and your headquarters may well have some programming for that.

This depends on campus culture, doesn't it? If the sorority is, for example, holding most of its events in bars and providing ID's to underage women, you can't get angry when they drink. I'm not saying that's the case here, but I'm saying that underage drinking needs context.