Jim 63,
I just bought my wife new OC spray and decided to go with Kimber Lifeact, as it is a "charged" propellent. This allows two shots, from any angle or position. From experience OC is not the golden savior, but its a darn site better than CS, CN, Mace or the earliest "tear gas" products. Although I personally have never had a problem, I have heard complains that several of the aerosol type dispersion sprays, don't work well when held upside down or in anything other than an upright angle. Limitation for the Life act is two shots, plus is that its a charged spray.
In any case, most definitely have your wife take a course or receive training from a person in the correct employment of this defense tool, and also... make her part of the decision what to buy as she'll be the one carrying it.
One more thing... if she is uncomfortable with any situation, the pepper spray belongs in her hand and not in her purse!!!!! If her purse is anything like my wife's, she'll never have the time to find it, let along deploy it.
Just my 2 cents...