I really wish I could help but I honestly don't know anything about this type of offence, other than in England you can sometimes get off on a technicality e.g. police time barred for failing to issue notices within time limits etc.
My advice would be, tell your wife to dress smartly, be concilliatory and keep her fingers crossed. And in future keep a diary of who is driving the car on what days! Never hurts to be able to deny liability
