I think I'm going to finally cast a vote here, and head down the path with 2Tim. I smell a rat and it's of the passive-aggressive variety. Maybe because I know all too well how those types operate.
IF this were a P/A action, I can promise you that giving in to the game will terminate it immediately. Consider it your "go directly to jail" card. If you tell her you've found it and read it, instead of her feeling relief, she is going to get angry instead....
Blaming you for snooping and not respecting her privacy. And then you'll be accused of a whole new laundry list of sins.
I have to award you an Oscar for continuing to act AS IF you had not read the letter. Since she didn't give it to you to read, I think it's best to pretend that it doesn't exist. And keep focusing on the things that have and do work for you two.
My two cents worth... which may not be much.
Hugs to you,
Betsey
"There are only 2 ways to live your life. One is as though nothing is a miracle. The other is as though everything is a miracle."
Betsey 
