When states have (or had) discretionary gun carrying license system, they have often provided that people who engage in “business activities that involve heightened risk, such as the need to carry cash or other ‘street valued’ commodities” should generally get licenses. (See this post, for instance, about the Maryland scheme.) The theory is that these people are at heightened risk of robbery, and the loss to them from the robberies is likely to be especially grave. And this theory seems factually plausible. To my knowledge, no-one has quantified how great the risk tends to be, or required such an empirical showing to justify creating such a category, but it’s certainly reasonable that the danger faced by someone who routinely carries lots of valuables is greater than that faced by, say, me.
But women, especially young women, are particularly likely to be targets of rape. See, e.g., table 4 of this document reporting 2008 data and table 4 of this document reporting 2007 data, reporting an aggregate approximately 0.5% per year rate of attempted or completed rape or sexual assault for women age 20 to 24. This is likely not as high as the attempted or completed robbery rate for men who carry valuables, but it might well be comparable when you multiply probability of the crime by the gravity of the damage to the victim.
In a sense, the women are transporting something that is likewise seen by some criminals as especially worth taking — their bodies. When people who carry lots of money are entitled to tools that help them protect their property (and also help them protect themselves against the death or bodily injury that may stem from attacks by robbers), why shouldn’t young women be entitled to similar tools that help them protect their bodily integrity (and also help them protect themselves against the death and further bodily injury that may stem from attacks by rapists)?
Of course, I recognize that if young women are allowed to carry guns to protect themselves against rape, it will be politically difficult to avoid extending the same right to older women, and politically and constitutionally difficult to avoid extending the same right to men. Thus, the licenses given to people, mostly relatively rich and mostly men, to defend against robbery will lead to less gun carrying than licenses given to young women to defend against rape. But is that basis enough to allow the money-carriers guns to defend against a less serious crime, but to deny the young women guns to defend against a more serious crime?