UF Anna, you've brought up a really interesting conundrum for Germans. But hey, congratulations on paying off that World War I debt! It makes my credit cards seem utterly manageable. If Germany can do it, I certainly can.
I'm interested to hear how you work through this issue. Since Tri-Sigma wasn't able to make it work, my guess is no other NPC sorority will be trying it any time soon.
I was just thinking, you might look into FAWCO, the Federation of American Women's Clubs Overseas. It's not a sorority style group, but you might enjoy continuing your connections with American Women. It's a worldwide group of expat clubs and I'm sure there are some in Germany. The website,
www.fawco.org should be able to help you, although it's a little hard to navigate. Some clubs allow a certain percentage of non-Americans and others have no restrictions whatsoever.