I became a OC instructor in 1997 (Freeze/Aerko), went to Defense Technologies in 1998, Freeze Aerko in 1999, and Ed Nowicki's OCAT Instructor Trainer Program in 2001.
In my experience, that is a myth about the lighter skinned folks getting hit harder by pepper. I've trained approximately 500 folks in use of OC and OC/CS products. The whole experience of pepper is largely dependent upon the perspective of the person being sprayed. If they think it is effective, it is. If they think that they can fight through it, they will.
The product really doesn't matter, as long as it is designed for law enforcement use. The technology to make pepper spray can be in a garage and a lot of it is slick marketing. Percentages of OC, SHU (Scoville Heat Units), the Carrier, spray patterns, flammability, and others are all things to consider.
The most effective spray I've used is FoxLabs 5.3 Million. It has a coarse stream and good distance. Second is Aerko Products freeze +P. Third is the Defense Technology MK3.
The key to making your wife comfortable with the pepper route is to buy two cans, tack up a paper plate on the side of the house and make her spray and move. If she gets a little OC on her, make sure that she soap and waters it and does NOT put cream, lotion, burn ointment, etc. on it. OC is a good intermediate weapon, but can't stand alone in place of a good mindset and effective tactics.
I carry a 1/2 oz key ring Freeze+P. It is a good intermediate between hands and the pistol.