It's probably been said... But it is better to have it and not need it than vice-versa.
Also, an FBI statistic is that one in four people will be a victim of a violent crime in their life, or know someone that is.... And crime grows 90% faster than the population.
Also, as economic times get rougher so do the desperate measures people go through in order to survive (or get money). Get a firearm, get trained and make sure your wife is, too. It is one of the best investments money can buy. If she still can't see the benefit, ask her what she is supposed to do when the man kicks the door in at 3am and you've got a baseball bat and he's starring back at you with a shot gun or a hand gun? Average response time for a law enforcement official is 12 minutes. If I recall correctly that's if an alarm company forwards the call to the police station. People use the excuse my neighbor is a cop, too. I can wholeheartedly tell you that I would never want one to try to defend my life. I am not saying there are not good ones out there, but the majority that I have trained have had better use as a shield for me from incoming fire.