Her one wish was clairvoyance. She needed it, she needed it so bad - it was the only thing that could soothe her constant fears. And clairvoyance is indeed what she found.
It almost worked the way she wanted it to.
Everything was clear to her: she only needed to focus, and the answer to anything would come to her with perfect clarity.
Scared of death, she only wanted to know how to become immortal. That, of course, she learned. And apply the knowledge she did - so that she would never, never die.
And immortality, by definition, is eternal. She had known it, yet failed to reflect on what it would mean. She's not truly alive like she used to be, breathing and feeling the ground beneath her feet. Yet she lingers on, unable to ever perish.
Now, she is forever haunting the mists somewhere between death and sleep, knowing she will never achieve either one. And she knows it with the same painful clarity with which she knows it is all her own fault. She has become eternal, and such is her suffering.