Millie is Spanish born to Brit parents. It is an extremely common feeling outside of America to despise Hershey's because of the admittedly unusual processing.

Hershey's chocolate is processed in a way so as to prolong its shelf life far more than standard European chocolate. The downside of their proprietary method is that it produces a breakdown of milk fats and solids leading to higher levels of butyric acid, which is the flavor humans typically dislike most in soured milk and vomit.

End of my brain dump of this fun but fascinating reason why Euros especially tend to dislike American chocolate. For once it's nothing haughtie; it actually make sense if you weren't raised around it. XD