I would question this. What exactly is your source for this information? If it's the book by Tim Graham that's not a reliable source as he's a royal photographer not someone with inside knowledge. It would be hard for QE2 to have any strong friendships amongst the European royals as she rarely sees them, QE2 doesn't attend any funerals ( except Badouin's) weddings, christenings, anniversary parties related to European royals,(Philip's always gone and now one of her children go) nor does she holiday with them. Even when Philip's sisters were alive Elizabeth rarely went to visit them, (Philip often did) his sisters did come to the UK and Elizabeth spent time with them. QE2 has cordial relationships with all the various royals brought about by official visits and the 2 Greek weddings she did attend in London. She also hosts various royals during the time they are in the UK (eg lunch before Charles' wedding blessing) but to say that she's good friends with any of them would be stretching it.