"Truth is one; the sages just speak of it in different ways."
Is this a child? You might tell her to write her dreams out on paper upon awaking.
Have you tried this, yourself or with someone else, PSH? How did it work out?
No, but I have read that everyone dreams—and that if anyone doubts that he dreams, the thing to do is to have him write down what he remembers immediately after awaking.I was thinking that the thought of being unconscious might be unsettling to her—too closely resembling annihilation. If so, the knowledge that she dreams might be comforting.
An interesting idea, worth trying.
P.S.H.'s method is also used sometimes to induce lucid dreams. This gives the dreamer (1) knowledge that she's dreaming while she's dreaming; (2) control over the "dream world"; and (3) the ability to wake up at will. All of which, I imagine, would be sources of comfort to a person who harbors the fears you describe.