"She has done nothing out of the ordinary. We all eat the same food and drink the same water. If she is sick from any of that, we all should be."
As you examine the girl, you get a gut instinct that this is no mere sickness. The girl appears to have been poisoned by some method...a very slow acting poison that is mimicking many of the signs of sickness as it slowly kills her. Such a poison is not common, and you have never heard of an herb or plant that by itself would have such an effect.