etienneSAI, i wouldn't give her the advice to just "stop going to things, stop voting, and refusing to pay dues..." because depending on the sorority ths could have major repercussions!!
in my sorority we sign financial agreements after becoming a sister which state a specified fine if a member does not go to a specified event without getting permission to be absent... this agreement also says that the chapter can hire a collection agency in order to collect any unpaid fines or dues from the member. i know this may sound harsh, but atleast we have always been able to obtain our money from "sisters" that have stopped fulfilling their membership requirements... so, find out if your chapter is able to do any of this before ending paying dues altogether!