What is the evolution of Sylvia's character in "The White Heron"?

At the beginning of the story, she is a shy, rather
uncertain girl who is easily impressed by others, and willing to do things to gain their
approval.  She is also rather naive and innocent, with very little exposure to human
frailty, greed, vice or cruelty.  She has led a rather sheltered life that has protected
her from having to deal with the reality that humans can be bad people
sometimes.

All of these traits come out when she first
meets the rather mysterious and handsome stranger in her area.  She is a bit intimidated
by him, wowed by his newness and ways, and very eager to please and help him. She wants
to impress him and make a good impression; her impressibility comes out, and her
uncertainty.  However, as she learns more about what the man does, she internalizes it
and realizes that she is going to have to make a big
decision.

It is when he wants to find the heron that we see
some real changes develop in her.  In her final decision to protect the heron over the
man, we see her more confident, assertive and willing to forego the approval of someone
new and exciting in order preserve someting more sacred and beautiful.  Her innocence
and naivety have been replaced with the knowledged that there are people out there who
are willing to destroy nature and make bad decisions. She shows great strength of
character and maturiy when she decides to protect what she knows, in her heart, to be
more important.  Her uncertainty is gone; she is certain, a bit more wise, and confident
in her principles.

I hope that helped a bit; good
luck!