I carry a PM9 and my wife carries the CM9. I have carried larger and smaller pistols and for me the PM9/CM9 guns strike the perfect balance. My wife moved from a Ruger LCP to the CM9 and likes it a lot more but it has been considerably harder for her to carry it concealed. She thinks it was a worthwhile trade off because she can shoot it considerably better than her LCP.
That 1911 looks enormous in her hands! Wow!I've owned and shot both. If you like one, you will like the other. You are right in that the key difference is the magazine/grip size. That little difference in grip size to handle the larger mags makes the following differences:
1- The larger grip area allows for an easy three finger grip. Some people shoot fine with a two finger hold. I do much better with three.
2- Both can be pocket-carried, but the CM9 is much better for that purpose. The CW9 can only realistically be carried in jeans or cargo pants pockets.
3- One more round may make a major difference in a very bad day. Compact guns are always a compromise on capacity.
If you don't intend to pocket carry, then just go with the CW9. It is easier to control and better capacity. If you do want to pocket carry regularly, then lean towards the CM9.
A couple of additional details since you mentioned your wife shooting it. She should also handle them and make sure she is comfortable with the feel. Since the Kahr has a smaller grip, she will probably be fine with it. The other thing is that the Kahr is designed to use strong springs. That can make them fairly difficult to rack. The good news is that this can be overcome if you use the right technique.
http://youtu.be/kbayNc6D9HY