As a former gun shop owner who has seen his share of heartache (from both the husband and wife) and trade-ins...my advise is to take a class together and rent or borrow some firearms and let her select what works best for her! If you both have already attended the CCW course then attend the next level where you train and practice fighting together with handguns (as opposed to learning about safety and the laws). Attend an 8 hour or longer class where you train seriously for self defense (as opposed to just range shooting) and consumme 300 rounds or more in a day. At the conclusion of the class she in particular will have a much better understanding what is fully involved in handgun self defense and what handgun will help her be successful in a lethal confrontation. After attending a class and practicing, for example, clearing a Phase Two Malfunction she will have a much better understanding what she needs in a defensive handgun to clear a handgun under stress.
We guys generally don't pick shoes out for our ladies so why would we buy them a personal defense handgun? Selecting a handgun is very personal and not something one person can buy for another....and do we really want our ladies to buy and use a handgun based upon the recommendation of a chat room commando by the name of "Six Shooter Extreme or Master Blaster 45" on some forum? No offense...but this is a very personal and important decision - potentially life saving and altering..she needs to be involved in this decision and not us!
When consulting with her for a selection you should weigh these variables in this particular order:
1st Consideration: Narrow the selection down to "proven reliable" fireams (this means firearms that have consistantly proven themselves on the street in all situations, weather conditions, and fighting situations). Keep our opinions and bias's too ourselves but give her some choices based upon what LEO's are using and have a proven track record of reliablity and stopping bad people...i.e.GLOCKS, Sigs, H&K, S&W, Kahr, & Kimber just to name a few.
2nd Consideration: Encourage her to select from handgun choices that "fits" her (not you or any of the other fellas on this site). Fit must mean she can reach & manipulate the controls with the master hand, reach the trigger without compromising her master grip, and sits well in her hand. Selection also means a handgun which will support her in mastering the "C&C's" meaning she can shoot and fight Competently and with Confidence. Of the two "C's" confidence breeds competence. If she selects it and likes it, and has confidence in it (vis 'a vis 'ownership') then training and creating conpetence now becomes considerably easier and faster.
Final Consideration: Caliber - anything above a 9mm gives her a fighting chance since all handgun cartridges are largely ineffective in stopping motivated human beings. Today we see 98 pound (soaking wet) 23 year old female recruits successfully completing Police Academies with no choice of what they carry, train with, or use...generally they are issued a full size GLOCK in 9, 40 or 45 and have no say or input into their choice of duty weapon. Literally hundreds of women graduate weekly after successfully training and qualifing with a full size defensive handgun...training and using a handgun is more mental than physical...if we tell our ladies "honey, that is too much gun for you to handle" then IT IS. If you tell them "honey, you can easily master any of these calibers with no problem...female LEO's and those in the miltary are doing it every day" then they will have the assurance and confidence they can master this technology.
Ah, but what the heck do I know?