Is your friend a girl or a boy?
As I've had no problems what so ever in Europe with ID and I've been going out and about there since I was 16. I have no recollection of ever being asked for ID anywhere in Europe. I've generally always been travelling with just one or two other girls, whereas I know my guy friends have had more problems in places such as Prague and Amsterdam mainly because they look like a group of young, rowdy, British lads who were just wanting to get wasted.
If she is a girl, you might be better splitting up when you go into places and she should go in more on her own with one or two other girls. Even if he is a guy it might be better to split up and go for small groups rather than all enter in a big possy as then you do just attract attention to yourselves.