I figure she just really improved her posture.

Fantasy elements like magic powers and dragons can be added to the world, but changing fundamental facts of nature doesn't make sense if it doesn't serve a narrative purpose. For example, a person who is cut should bleed. If a person is killed, it is understood that they die. Puberty takes place during a certain age range. Deviating from these facts will be met with audience confusion unless it is reasonably explained