Against all odds, despite Ashley having gained a lot of weight after her romance with Thomas and her breakup, she seems to have gotten stronger, now being able to lift the farm tractor with one hand above her.
Mox simply can't understand how this is possible, especially since his daughter has gained a lot of weight and doesn't do much sport, except working on the farm.
Nancy, her other mother, theorizes that it's possible that her enormous weight is allowed to strengthen muscles in her body to adapt to this new lifestyle, the time to lose weight, combined with the physical effort on the farm and genetics, would give Ashley great strength.
But for the moment, there is no rational explanation, as much as science or magic could try to explain that explains how Ashley is even stronger. A real mystery.