There ought to plenty of opportunities during the mediation meeting to exhibit some 180's--maybe get in some affirmations, show as much calm as you can.
I know how you must feel--you knew it was coming, but you were hoping...Still, remember how long this process can be. You're trying to change someone else's mind, mainly by your own actions--but also by allowing that person the freedom to explore life without you.
Your wife seems to take a certain pride in her commitment to her word and the relentlessness of her follow-through. So mediation she must have, if only for her own pride. She is probably still serious about separation, but there are a lot of good signs for you, as well. You have to work on strengthening the doubt which I am sure she is already feeling.
It's impossible to know what someone else is thinking, but it's interesting to speculate. I sense that your wife is less sure of her course of action than she was when she wrote you the E-mail you've quoted. And even in the E-mail, she sounds like she's trying to buck herself up with severity.
So just you go into mediation like a DB warrior. You're a natural (except for sleeping through dance class).
By the way, I think I'll try your technique next time I have a whiskey bottle in hand. I'll just go read about George Washington.
