Give me a break. They're getting in trouble just because they're a sorority. I'm sure there's a ton of non-greeks who keep their old notes, tests, and papers and give it to their friends to use. It's not a big deal. I don't find it to be cheating. Cheating would be bringing these notes or tests into an exam with you. The only things these girls are doing is using these old tests to study from. If the professor is too lazy to change the exams every semester, then that's the professor's problem.
ETA- Looks like honeychile was typing at the same time as me and said the same thing about lazy professors.
I knew a lot of them in my days. We had a few tests on file from back in 1997 and when I took an exam in 2002, it was the SAME EXACT TEST...nothing changed. You would think these professors would change their lesson plans over the years to reflect changes in research or trends.