Where to begin...
You say "I certainly like to look nice when occasion calls for it". I'd say recruitment calls for it.
Pick out a couple of nice tops and some slacks or a skirt, a pref dress, maybe just some lip gloss if you're not that into makeup, and you're set. Probably some of the sisters you're going to meet would also prefer to be lounging around in casual clothes, but they're going to put those clothes aside in favor of their recruitment outfits.
I went to a northern school too, and recruitment (even formal recruitment) is more laid back than it is in the south. Still stressful, but maybe not as stressful as recruitment at, say, LSU or Ole Miss.
One other thing: Discretion is important. The internet is a lot smaller place than you might think. Just something to keep in mind.
Good luck!