I've had my share of bad gigs, but I would not go into one accepting that it will be bad. I think there may be ways to redeem this one, if you're willing to try. It's certainly worth a try.

My wife comes to a lot of my gigs; her presence does not detract from my performance, so I disagree with troll's suggestion that leaving her at home is the only professional thing to do. Also, she knows me and my music well enough that she will not think less of me if I turn in a mediocre performance. I suspect your wife knows you well enough to overlook this, too. So why ask her not to come? Are you embarrassed? I would think there are a lot of people that I might be embarrassed in front of, but my wife is not one of them.