My chapter just started doing "senior status" when I became a senior, and it was, quite frankly, totally awesome.
Seniors still had to go to meetings (I think we would've all gone anyway even if we didn't because we wouldn't have known what was going on otherwise), but we were excused from other Greek events and not penalized. Everyone who had enough credit hours for senior standing at the university was granted senior status in the sorority, regardless of how many years they had been an active member. I'm not sure why you weren't granted senior status, unless your chapter's policy is different than ours.