Do you remember when you were a kid, heading home from somewhere, knowing that when you got home you were going to get in troube for __________ . And the closer you got, the more worked up you felt?
Your wife is feeling anxious because she doesn't know what to expect, and dear gawd, what would she do, what will it mean if the shrink looks at her and tells her she ISN'T normal? C'mon. Encourage and support your wife. This isn't about you (though it sounds like you are taking it that way). She is NERVOUS. Tell her the shrink is there to talk to and will help her discover things to talk about that she would never imagine. Don't let her off the hook, but give her the kind and encouraging words she NEEDS from you to find her own courage.
btw, why do you not help your wife with running of the kids? She went out no less than 4 times last night and you are wondering why she didn't sit down with you until 10? Really?