Not a lame question. I think your choice depends on 1) your wife's attitude to use a weapon, 2) you wife's ability to use a weapon, 3) what kind of car does she drive and 4) should there really only be one weapon to rely on....and then there is the local law thing to ponder. For instance, my wife lost a sister to a car-jacking 35 years ago so she has no problem with any level of self-defense. She drives an old Excursion which allows for some additional interior room to consider for options. The height of the vehicle puts the level of her attacker more at head level where the attacker is looking straight at her as opposed to downward in a car so he can't see so well what's below the window pointed through the door below the glass at his mid-torso. In this instance she can have some safety of the glass being up making an edged weapon a secondary choice because it can't be used through the door...which will normally be the case for any vehicle short of a convertible/t-top I suppose.
Ability...my wife just likes her Glock and Kahr so one's holstered between the seats and another she carries. If I could talk her into it, the Glock would be replaced with a Taurus Judge with 410 shells in it because she's 6' tall and can handle the heavy Taurus...a slight woman may not be able to use the Judge effectively.
Just my 2 cents.
EDIT: You two should consider multiple forms of defense. For instance, less lethal like pepper spray when lethal force is not called for. What Tom said below. Using the car as a weapon is possible is another form of defense that does not take a gun...just the right situation, etc., etc.