Here are some things that were helpful for me, in making the transition from ardently anti-gun to packin' mama:
-The NRA Basic Pistol course, taught by an exceedingly safety-oriented instructor. Your wife should take this class or one like it. Even if she never touches a gun again, she needs to learn how to safely operate the one you have in your home.
DO NOT, repeat DO NOT try to teach your wife the basics of gun operation yourself. By all means attend the NRA class along with her (then you'll be able to talk about it conversationally as she likes afterwards), but do not try to be her instructor. If she needs one-on-one attention, let someone else provide it.
-At the NRA class, and at the range afterwards if she is willing, have her use a gun she can comforably shoot (even if it's "only" a .22). I hate my husband's gun. I can barely reach the trigger and the metal corners on the frame cut into my hands. If he had tried to convince me to shoot it regularly, I would have absolutely despised shooting. But I fell in love with target shooting by using a gun that fit me and my skill level.
-Allow her to enjoy target shooting without committing herself to ever using a gun for any other purpose.
-Allow her to disagree with you on when it is acceptable to use deadly force in self-defense. Have her explore her feelings about using deadly force without it being a "gun" issue (there are plenty of other deadly means of self-defense).
-Talk with her, at appropriate times, about when exactly you think it is appropriate for you as a civilian to actually use your gun. Discuss various real-world scenarios (taken from the crime pages), and go through a what-would-I-do analysis. The big thing here is that if she learned about guns from TV and movies, she's seen a lot of gun waving, gun tossing, "I have a gun announcements", etc. [There is less drama in a gun that is safely concealed, drawn only to shoot, hits its target, and is immediately reholstered.] She needs to understand that you are not going to operate the gun in reckless Hollywood fashion, but only under the most extreme circumstances, after determining that the gun is the proper response to the situation.
-Review cases of accidental shootings, and discuss how the various principles of safe gun operation were violated. Explain to her how you are taking the necessary measures to keep unauthorized users from acessing your gun (you'd better be doing that!!), and how you are preparing your children to act safely if they should ever, heaven forbid, be in a "kid & gun" situation at someone else's home.
-Demonstrate to her that you are a safe and competent gun owner. Be safe and competent in the rest of your life as well. If you have a temper, now is the time to get it completely under control.
-Give her time.