I mean, yeah. The idea of an unknown disease or virus from another world entirely is dangerous on an unprecedented scale. That's a place with magic, for christsake. A strain of bacteria or disease from her world being completely different from any known strain in the world is not only possible, but likely. Hell if the disease had anything to do with magic (aside from people who have less magic being less susceptible to it) it'd basically be game-over for the entire world.
This reaction seems like the natural response imo.