Trans super-per-day #439: Mokele'! From the Whateley Academy universe, Portia Smith is a junior at the titular school, her mutation having caused her to gain a male body and she now goes by the name Peter. Despite being referred to by male pronouns in inferences I've found, it's also stated that she's not happy with her transformation, which points to her not identifying as male in actuality. She's listed as a villain on the wiki, though I don't know how she is, due to not having read the stories.
Mokele has the ability to shapeshift into various animal forms. However, unlike some shapeshifters, she can only increase her mass incrementally, an example given on the wiki being that if she wants to become a dragon, she needs to transform into a panther, to a bear, to a rhino, finally to a dragon. These transformations are more than just altering her appearance, as well, as when she's a dragon, she produces venom valuable to mystics.
It should be noted that I didn't see anything stated as to her appearance, so the above picture may be quite off, being completely designed by myself (with a Whateley Academy male uniform). Not that it's well drawn in the first place.
The Whateley universe can be found here.