Dunno if some of you already read this article ? http://espn.go.com/tennis/story/_/id...-play-olympics
It clearly explains why Marion will never make herself available for fed cup without her coach. Because he is the only one to know when adjustements are needed for the next practice sessions and which drills could be changed. As he said :
"My approach is quite different, because I'm not a tennis player". For example, "The shoulder, I view in a mechanic way," he said. "The shoulder of each athlete is completely different, so you need to take care of every specific thing, purely mechanically, for each athlete."
"you know, it's very important to be confident in the way that you practice," he said. And Marion's confidence is only for her coach, and anyone else.