As others have said... Training classes will go a long way to helping her out. The women only classes are awesome, because they focus on the unique problems that women may experience when new to firearms.
As far as what pistol... Any full size or compact (think glock 19 size) pistol that fits her hands well, made by a respected company, will work well.
I can't stress "fits her hands well" enough. Also a pistol with sufficient grip texture, so it does not slide around under recoil.
When my fiance was first learning, she loved the PPQ feel in the hand, hated the slick feel under recoil... She has gained experience now, and does not have this issue any longer, but it was important to her then, and to this day, that the gun feel secure in her hand.
Price is where you have to look around a bit, as there are many good pistols in the $500 and up range, $400 and less is harder.
The S&W SDVE series works well, but the trigger not great. It's long and heavy... Which reeks havoc on new shooters and those who do not practice often.
I hear good things about the Walther PPX... Despite its questionable looks.
Neither of those have adjustable grips though.
I am a fan of CZ... And hear great things about the P-07 gen 2... (gen 1 is good, but some improvements in gen 2 are nice)
The only issue with CZ is the short slide can be problematic for some people. My fiance can use her CZ at the range, but I would not trust her ability to clear a malfunction quickly during an emergency situation.
If your wife can not easily and quickly manipulate the slide on the CZ... Or any pistol... Then search for another.
I wouldn't worry about mag release and slide stop position too much... As I can't reach the mag release on almost all pistols, without adjusting my grip... And that is fine.
I actually started moving my mag releases to the opposite side, due to my love of the paddle mag release on the new German guns... I use my trigger finger to drop the mag, with no adjustment to my grip for reach.
I have seen S&W M&Ps on sale for around $400... Not a hammer pistol, but the trigger will not be overly light or short.
SIG 2022... Can be had for around $400,but only one mag in the box... And extras at near $50 each.
The Canik TP9 is DA/SA... Very Walther P99 like. They just made an updated version gen 2 that improves the pistol.
The TP9SA is a lighter trigger, and may not be a good bet at first.
Thinking about it... The TP9 may be the best way to go...