Catzenpewters-
But if she won, wouldn't the old man just find another victim? 
Maybe this time it would be Sam! Someone else, maybe many
other people, would have to go through what she was going
through. And maybe she could stop that, end the curse. 
Maybe that awful old man would have to stay old forever.
But if the riddle was so hard, and she couldn't answer, then
she would lose and have to switch places with him. Surely it 
was better to take the good chance to save herself, than probably
fail the other riddle and help no one?

Come, girl, Tom growled gently.  I will take you where you need
to go. You may make your decision on the way.

Dreamer_on_ice-
As they walked Sharon thought and thought until it seemed her
head would explode from all the pressure.  Then she heard a 
familiar giggling sound from above and, looking up, saw some
of the flower folk like those from the giant stalk floating down from
high in the sky like sentient parachutes.

What?!?, she remarked.  The wolf too stopped and looked up at 
the happy imp like flowers as they floated gently downward.  
His eyes glinted for an instant with a hint of a red glow and for
just a moment Sharon thought she imagined she could almost 
smell something evil in the air, something very old.

Then it was gone again quickly as if it had never been but 
afterward the sun didn't seem so friendly.  The light seemed colder
somehow.  An instant later the screaming started.  The thicket around
them had again sprouted thorns up in the top layer and the flower
creatures were being impaled on the long thorns as if in the points
of spears.  It was a horrible sounding scream they gave out as they
died and the thicket ran with sticky substance which Sharon assumed
must be coming from the dying flowers.

As she watched, the sky darkened and lightning struck nearby with
a mighty snap and clap, leaving her frightened.  There was a hint
of the smell of brimstone in the air, a sulphurous awful smell.  
The bodies of the flower creatures writhed on the thorns and imp like
creatures began to emerge from them like insects emerging from a
cocoon.  They were gory evil imps and they scrambled to the ground
and forming a ragged line of sorts, began to walk slowly and 
deliberately towards Sharon and Tom.