Jeff, I would sit back and just watch the drama unfold. I would keep my expectations at zero at all times. They do tend to bounce back and forth w/break ups and getting back together again numerous times. So, unless she's further along and really ready to face her demons, she's still going to be on the emotional rollercoaster a while longer.
I think it's a great opportunity for the two of you, if you could go out and purchase a gift together. It's a step in the right direction and doing it as "friends" is the first step towards her realizing what she's left behind.
Just be yourself, have fun and no expectations. To look at it another way, it's a "fun" date and who knows, a cup of coffee and a pastry just might find their way into the schedule. Treat her as a friend or a co-worker and not your wife. No talks of the relationship...this a "fun" date. Keep it that way. Patience is the key today.
Have fun!
Sit quietly, the answers will reveal themselves when you least expect them to. The past is gone, the present is a gift and you need to focus on today, allow the future to reveal itself when it is ready.