I still see you being railroaded. She writes a long letter explaining her feelings and desires, and expects you to 1) move out of the house, and 2) go into mediation for a divorce, and 3) get over it.
Nice. Maybe, for her. Realistic? No.
It's your turn to say something. I think you should say, "I will consider mediation after we go to Retrouvaille with open minds and willing to try to understand each other." Note: I did not say, fix the marriage, reconcile, or any other phrase indicating a predetermined outcome for the weekend. I just said "open minds and willing to try to understand each other". Because, you both deserve that after 10 years and two children. And with a future relationship of some sort, that won't end in the foreseeable future.
She owes you 44 hours of talking to you about your lives. (And 16 of those hours are spent asleep.)