As others mentioned, if you give her to malager, you can get her to transform. Though anyone given to malagar will have their select scenes and then be gone forever when you get to act V I believe. So no Naho dragon girl after you've seen the malagar scene. to be considered dead and gone.
Honestly I think the thing that ruins this the most, as much as it makes it extra edgy, is just this. That so many things which are really fun, then lock out that character completely, they're now dead. Or just a permanent lab rat we can't have back. Yet for some reason, the most absurdly brutal example of transformation is the one Mr Dragon actually get's to keep,
little old stubby witch.
I feel like having the option to have a proper Harem, not choosing one consort but all of them if so wished, all three queens etc. and having the option of all the different transformations as keepers, not throwaways would make a lot more sense in terms of player enjoyment. Frankly the worst one is the one we get to keep so why not the rest of them which are for the most part more fun.
It's a dragon level power fantasy, why not more power fantasy shaped, we don't need realistic dragon fantasies...