I bought a 9mm P99QA back in November. This is my first handgun, but not the first I've shot. I must say it is absolutely fantastic. I wanted the AS trigger system, but I just couldn't find it, and 2nd gen P99AS didn't come with the OD green frame. The trigger style you pick will depend on your wife's handgun experience and preference. If she likes a consistent trigger pull, get the QA. It's about an 8lb pull, with a bit of travel, but after 500 rounds of break-in, mine shoots sweet, with a very smooth pull. Recoil is very light for a beginner shooter. My girlfriend has been spoiled by my P99, so eventually I'll have to find one for her, or give her mine. With the 3 backstraps, your wife should easily find a grip size to fit her hand. We both like the small size backstrap, and it just melts into my hand. Very well balanced pistol, in terms of weight.
This video will give you all the information you need about the AS trigger variant:
YouTube - Walther P99 AS Trigger
As far as reliability, I trust this firearm with my life, hands down. I know the bullet's going to go where I want it, when I want it, every time.
In regards to CCW, it's a little on the big side, but with a proper holster/belt combination, and the right clothing, it should'nt be too difficult to conceal. It's comparable in size to a Glock 19.
The only size difference between the .40 S&W and the 9mm version is that the slide on the .40 is .12 inches longer than the 9mm. My suggestion would be to see if the store has a holster they'll allow you to try on with the gun in it, just to get an idea of how concealed it will be. For what it's worth, I have little to no difficulty concealing with a light hoodie or zipper jacket.
Feel free to PM me or reply if you have any other questions.
P99 - Hell and back reliability, with a pit stop at the in-laws.
I promise I'll shut up now. :redface: