3913/p239
I've shot somewhere between 800/1000 rds. through the 3913 but, other than yhat, have little long term experience with it in terms of reliability and duribility. It seemed to br an adaquite weapon.
The Sig 239, however, Is another matter. I've owned one for some time and found it to be, for me, an excellent choice for a CCW carry weapon. Extremely accurete, highly reliable handgun that shoots smoothly and conceals easily.
If your wife likes both weapons equally and feels good shooting both weapons; based on my own experience only, I would not hesitate to give the edge to the Sig 239. It also seemed, to me, to be the safer of the two guns mentioned...
Either way; shoot safely and enjoy your choice...