You may never be able to convince them that sororities are not like they are protrayed in the movies and in the media. But you can show them by your actions that you haven't changed any and that you are getting so much out of your Greek experience. Treat them just like you were recruiting them to pledge Alpha Gam.
Talk about the scholarship focus we have - the number of hours you're required to study, the gpa you must maintain, the scholarships the Alpha Gamma Delta Foundation offers.
Talk about the philanthropic work your chapter does, not only for the Alpha Gamma Delta Foundation but also in the local community.
How about all the leadership skills you're learning - time management, empowerment, delegation, teamwork, public speaking, financial mangement (especially if you're an officer and have to work within your budget!), etc?
Share the experiences you've gained from meeting new women from different backgrounds and lifestyles - something you're friends may not get to do!
Lastly, you have sisters who have helped you to acclimate to college and their sisterhood and friendship has helped to soften the blow from being so far from home and your hometown friends.
You'll also find that as you go through college you will not have as much in common with your friends back home due to your collegiate experience (and I'm not just talking about being Greek!). That's part of life. But those hometown friends who are truly your friend will support you as you grow, just as you'll support them! I have only a couple of close friends from high school (I'm 37 now!) and the majority of my friends are from Alpha Gam, college, or work!
Don't be afraid to share your problems with your sisters - the older ones have probably been down this path too and can give you the support to make it through this frustrating time! Hang in there!
Loyally,