[Oldschool45B]

There are several cans that work 100% on the Beretta. I have an AAC EVO-9 and a YHM that work just fine on the SIG and the M9. They do tame the recoil a bit, but you get force pushing it back forward causing nose drop. There is enough threads on the end for the can, you just stop a fraction of an inch before the slide to keep the two from hitting each other. A decent gunsmith can do this without issue.

Here is the problem you will have with using a .45 can on the smaller calibers. Outer barrel diameter. Measure the outer diameter of the 45 barrel and then your M9 barrel. Pretty big difference. Unless you get some kind of thread adapter you are a no-go.

And this is just a recommendation from someone who has seen it time and again in the military and leo community. DON'T teach your wife to shoot. You can be a professional instructor but first and foremost you are her husband. Have someone else work with her.