Some of the things that are often mentioned here on Zaar and which I have never seen in Germany are:
:arrow:liquid smoke
:arrow:A1 steak sauce (even though there might be something similar, I can't tell as I don't know what A1 steak sauce is like)

graham crackers

bis-quick

butter flavoured crisco

velveeta

grits (but you can find cornmeal or polents in some shops)

any baking 'chips', apart from plain chocolate ones

meassuring cups, if she wants to use American recipes. In Germany ingredients are usually weighed instead of meassured in cups, so she'd have a hard time finding meassuring cups if she doesn't bring her own.
That's all I can think of for now. I'll post later if I think of anything else. I think your friend might get a shock at first going into a German supermarket, because she will probably feel that the choice is so much smaller. However, I think that the quality of food makes more than up for it and there are many smaller delicatessen stores where you can find special ingredients. Also, I think it is mainly the vast amounts of US convenience foods that are 'missing', if she likes cooking from scratch she won't have many problems I think. I'm always looking forward to go shopping in Germany, when I visit my family.
