I'd suggest a Retreat or a Chapter Forum. In our last chapter forum, we split up in 4 groups and discussed problems related to retention, spirit, involvement, etc. We then sat down and POSTIVELY discussed possible solutions. As someone who has been in your sisters' shoes, this gives them a good chance to air out some problems without seeming or feeling like a total *****.
I can say that if we had had that Chapter Forum a week later, I wouldn't still be a sister.