Are you really wanting out of the "greek scene" or are you just the average senior who is tired of everything
? I think there are many seniors who have been greek for 3 years that get burned out - I know this is true in my chapter. Our chapter (informally) offers a break to these seniors who are just really stressing over grades, graduation, job hunting, etc. They don't come to every event (except ritual and other events that are fined) and we just make sure to help them out so they can still have fun their senior year.
On the other hand, if a sister truly wants out then our organization can't really stop her. We have had sisters formally turn in their pin and resign, and we've also had sisters just stop paying dues and showing up for stuff. If you truly don't want to be an XYZ anymore, I don't see how they can stop you. But I caution you against this until you are really sure. If you do this you'll probably lose good standing in your organization which is usually important if you ever seek alum status. Many seniors later end up participating more in alum stuff than chapter stuff after they've had a chance to step back and chill out.
I just ask that you really take the time to ask yourself: am I just burned out or do I really never want to associate with anything dealing with XYZ? Please feel free to email me if you want to discuss other issues!