I can't believe no-one else can see it! (excuse the pun!) It is sooooo the blind 'red' haired lady!

I have re-watched the episode looking for this and the Tea Cup is continually featured throughout the episode once we meet her and then twice shown in front of the monitors 'Red John' used to view the cellar at the end of the show. She is not really blind, she is Red John... Their are enough pointers to show it! - I would be intrigued to see if she is in earlier episodes (in the background)...