Small to medium .38 Special revolver, or a .357 Magnum, which will also shoot the .38 Special round. Of course, this somewhat depends on your Wife's hand size and strength.
That is in agreement with some of the advice I've solicited among friends. I think that may be the way to go.
This is an excellent suggestion. If she gets comfortable with a magazine-fed, semi-automatic pistol, get her a GLOCK 19 or a GLOCK 26.
This is good advice. Revolvers are simple. Point and pull the trigger. I would add three things:
(1) I would recommend a hammerless revolver. The upside is there's nothing to snag pulling it out of your purse. The downside is that if you are ready for a confrontation, you can cock a gun with a hammer and your first shot will probably be more accurate. After that, hammerless and with hammer revolvers are the same. IMHO, it's unusual to have time to cock the hammer and she will probably forget to anyway in the heat of the moment.
(2) Get a weapon with a ported barrel, especially for a woman. A well ported gun hardly jumps at all after you fire a round. So your second and third shots are WAY more accurate. Also, it will be a lot easier for her to get used to.
(3) Unless she's strong, a .357 is probably too much gun.
Also, remind her that an automobile is a mighty weapon. If someone is crazy enough to be threatening and standing behind the car, all she needs is forward or reverse, depending on her judgment of which leads to a safer solution. Getting out of your car because you feel protected because you have a gun is frequently not the optimal response.