I'm sure she has a really solid background story. Somebody close to her, might have been killed by a monster. That's just a tad better, than somebody dying cause of food poisoning and now destroying all food. Or somebody dying in a farming accident and now forbidding any kind of food production and means of acquirement, because it is dangerous. It's still stupid.
Well...if she gives a valid reason on the other hand, like, "Researches/experiments have shown, that things like natural plants will sprout, that also carry food, once the monster population is gone.", well that would change things. But it's not very likely.