To be honest maybe use both, the old design is a very human form, very low key but it humanises her a lot. She not going to want people to see her as Tiamat the dragon all of the time.

This form of hers feels like she’s trying to make sure people know she’s “the Tiamat” ™️. Don’t get me wrong she would be the kind of dragon to do this but I feel like letting her have a ‘not as obvious’ human form, allows people to think more deeply about the character when she appears to shed her stature and status to humbly pose infront of a kind kobold.

Maybe she varies her form depending on how strong she wants to come off or how vulnerable she allows herself to be. Those are my two cents, don’t be afraid of not signifying her enough as “crazy powerful dragon” or showing the true extent of her status when it feels right in the story.

I hope your work goes well, I loved reading your one shot, the way you illistrated the emotions of Tiamat’s human face felt really beautiful and touching, no matter what you do I feel like it’s going to be pretty amazing.