To my own experience lighter 9mm autos (like Glocks and Walther P99) give more easily problems with limp wristing than heavier guns. The exception might be HK USP Compact; it is light, but at least mine works well even when held loosely.
Since your wife has that problem with Sig 226 that gun probably does not fit comfortably to her hand. Gun/shooter-fit is individual, and something that feels comfortable to you might not be that for her. I know that some small-handed persons use guns with large grips very well, but to others that makes big problems. The other thing is recoil; people might limp wrist because they anticipate recoil they experience uncomfortable (that feeling is also individual), and therefore I think a hotter load is not a solution, a milder might be (if that gun is reliable with mild loads).
Since you ask about 9mm and .380 that is probably the level you wife can handle quite comfortably. I think you should look for guns that fit well to her hand; that might mean grips with single-stack magazines, or compacts with double-stack. Also, the gun should not be too light for the recoil to avoid limp-wristing. I think you could try 9mm HK USP Compact, and compare it to .380 Beretta and Taurus models of nearly same size. If problems come even with the 9mm USP Compact a .380 that is relatively heavy to the caliber (but not heavy to hold) might work.
Ossi