What did the note say?

Just before Edith murders her sister, she places a handwritten note in Margaret's lap and tells her "This is why I asked you to come here"....Any ideas what was written in the letter? She already got Margaret to confess that there was no child, so that was already out in the open. Edith also told Margaret how that lie ruined both their lives, so I can't think of anything else the outspoken Edith would want to tell her sister in a note and not vocally?