My Take on this Movie
I just watched it tonight, and it was a pretty good movie. :) I felt bad for Charlotte throughout the film, and when the planter fell on the couple, I was glad because they were terrible to her....they got what's coming to them. :)
As for the ending, I feel it is open to interpretation. That letter is to free her of the 1st murder of her lover (not for the recent murders), and she is probably taken to a mental institution....I feel she did it in self-defense since she knew they would try to hurt her again. Obviously the older man who gave her the note at the end will help her out, and incriminate the evil couple....since he mentioned to the reporter about them.