Hi!
I actually know of a few other similar situations. I wouldn't worry about it too much as long as they have your correct address. Although it's probably better to change it now before it gets more messed up and you get on the "LOST" list.
If most of your friends and sisters know you with 2 last names then use them both. You may want to consider just for AGD purposed, using a hypen for both names to make it one word or if most of your sisters just know you by one last name, I would just use that one. If you want to use both last names as last names, just be sure to tell them specifically what you want listed for your first, middle, and maiden/lineage last name and make sure they don't have you listed as an alum. I think I received alumnae information in college, so they may have you listed correctly, but definitely double check.
I would try updating your information on the website first - (under member services)
www.alphagammadelta.org . It may take a few days to show up on the online database. If that doesn't work try calling or faxing a letter (phone: 317-872-2655 fax: 317-875-5824). I could be wrong, but I believe Audra has already retired so I don't know if IHQ is continuing to check her email or if she is still checking it.