Unfortunately we don't have special stores with low protein food in Germany. What is your friend looking for?
In the PKU board you can find some products which are low in protein under "Products". Maybe this will help your friend.
We don't have such specialised shops. Food like pasta, rice and bread is mostly ordered from online dealers. Vegan cheese, spreads and cold meat can be bought in larger supermarkets and in the "Reformhaus", which is a kind of organic-health-food-store. I remember buying this gluten-free, low-protein bread (called Steinofenbrot from the company Hammermühle) in Berlin in a Reformhaus at the train station Friedrichstraße. As cheese I recommend the Wilmbersburger vegan cheese which has zero protein and is sold in many supermarkets. Ask, if you need more information. Tell us, what she/he needs exactly, this way we can make more precise recommendations.
Btw, the bread company sends out their fresh bread every Tuesday and in shops Wednesday, so your friend might be able get fresh bread tomorrow.