[Alumiyum]

We used fines (too much, IMO), but extremely poor attendance could also result in losing all social privileges for the next semester IIRC. It might mean you don't see drastic results until next semester, but as soon as a rule like that is enforced I guarantee it'll make a difference. Missing one event isn't the end of the world, but missing the entire semester can make people think twice.

You could also try doing what schools do and define what is an excused absence and what isn't. Genuine illness (with a doctor's note), university function, legal obligations, funerals...those are all some I can think of that my university considers excused. But what it doesn't include is "I have to study for my midterm tomorrow" or "my boyfriend is in town for 3 days". Possibly decide on the number of excused absences that are acceptable (like 3) and the number of unexcused (like 1) and then institute a punishment for failure to abide by the rules, including getting excuses in on time. Remind them that they are college women and neither school nor work puts up with wishy-washy attendance, so they should treat the sorority the same in that respect. If your excuse isn't covered or received in time, you get an unexcused absence and suffer the consequences.

It also is important to make sure it's just laziness that's responsible for the attendance problems. (Not that I don't believe you because my chapter had the same problem several semester and IMO 95% of it was laziness.) Ask sisters if there are things about the meetings or required events they would like to change (not including, of course, not having them).