I always try to subscribe to the "expect the worst, but hope for the best" philosophy, but find that I have a hard time holding both those things at the same time. My experiences, both personal and as a long time critical care nurse, tend to tip me over into the "expect the worst" side of things most of the time.
So, anyway, thyroiditis. It explains pretty much all her symptoms and her weight loss. Her thyroid is releasing too much thyroid hormone. It will take about 4-6 weeks to resolve. No real treatment other than supportive stuff like Tylenol.