A customer could mention something in passing to her former employer about how your wife is still in town opening up shop, yada, yada. Next thing you know you're in court pleading with the judge about how it's all okay because you have a po box 100 miles from here. Think he'll buy it? My guess is, no.
You cannot go to prison. It would be a civil matter, not criminal. You cannot pay a fine either. It is a civil matter, not criminal. IF they decide to take you to court, (A BIG BIG if), a court can stop you from operating, and even decide to have you pay money - if you are being sued to do so. It is a very rare thing to have this happen. Think of the expense and risk. The former employer may lose. Ouch. Best bet: Honor the agreement. Do not steal customers or processes. Start your own biz, but don't step on their toes for one year. After that, stomp away.