Why did she have to die?

Peter: But why did she have to die?

Mr. Barrie: I don't know, boy.  When I think of your mother, I will always remember how happy she looked, sitting there in the parlour watching a play about her family, about her boys that never grew up.
She went to Neverland.  And you can visit her any time you like if you just go there yourself.

Peter: How?

Mr. Barrier: By believing, Peter.  Just believe.