I also think she was drained of emotion. Like there was literally nothing left to give.
In addition to growing, getting sick, and whatever else, there is really no way to practice how you feel after winning everything for an entire season that is also your debut senior season. Beating your idol, training mate and friend at Euros. Then winning not one but two medals at the Olympics, winning Russia's first gold and becoming Olympic champion. Then becoming and instant hero/star/celebrity at home and internationally.
When it was time to do it all again for WCs, something just said - nope.