Look, I hate to take away from a well-written and important article, but this line is ridiculous. You can’t be “allergic” to your own blood, sweat, urine, tears, or milk.
I’m no doctor (or pharm rep!) but it’s clear that something else was going on. It’s both distracting and irresponsible to include this line that both conveys authority (from a pharmacy rep) as well as inconclusive and unproven diagnosis.
If you feel like it must be included, rewrite it to “Montalto noticed that the hives would worsen when she nursed, and she suspected that she might be allergic to her own breast milk.”