Lord Second Era
As seen in Episode Number 8, during Gyuki's flashback, Yuki Onna can be seen as a woman with both adult facial feature and height.
Lord Third Era (Now, Episode 1-...)
Now, Yuki Onna is as tall as human form of Sandaime and has kid-like facial feature, which is kawai :D.
HOW COULD THIS HAPPEN?
NOTE: I am asking HOW not WHY
Although unrelated, the reason why she did this might be something like this: