As a PPL of less than a week's standing, I am of course superbly qualified to comment on this -- and all -- matters aviational.
Much as it pains me, I agree with Gerund. I too was petrified of my QXC; much more so than the Skills Test. Why? Because on all my dual trips, I knew I had been helped in one way or another, whether I had asked to be or not. I simply did not believe I could do it alone.
I was sent off on a quite long "rehearsal", over unknown territory. Had to force myself into the aircraft and quaked off into the sunrise. Got horribly lost, or so I thought. (Was in fact only a few degrees out...) But ended up calling a friendly MATZ controller for a QDM. She gave me a QTE, which I actually started to follow, before the "'Ang On..??" mechanism cut in. We sorted it out between us.
Moral: It proved to me that I COULD cope, even in the face of my worst fear.
I would guess that getting lost is most students' biggest bugaboo.
My instructor behaved as if he had no doubt at all in my ability. That helped. But it would have helped more if, as Gerry suggests, previous incumbents had just sat there with buttoned lips, and let me generate a bit of confidence for myself.
Good luck to you and your student. First Solo, schmolo! Getting the ticket makes it all worth it.