You can be with the Dragon without needing the pink catgirl, but you still encounter a catgirl before you encounter the black ginger dragongirl. She is not the only Dragongirl. There is another you can encounter but she'll expect you to be heroic towards an elf or likely kill you. It is bit confusing because the ginger wears black and acts more like an actual black dragon, but the other dragon actually has black hair but acts more like an Onyx Dragon if you remember in D&D (Chromatic Dragons are Evil while Metallic Dragons are Good).
Yes because it's one of the many routes that branch off from meeting Regina
But anyway, at that time both dragon girls routes didn't exist. Back then gallery didn't have a menu, sections for each character but every picture of each giantess was in one big gallery.
I'm pretty sure that Seinaru (ginger dragon) was the first dragon and she at first didn't have her own route but was only available as a guest character after meeting and going with the Haramunia (pink cat)
Riys (black-haired dragon) with the elf girl come up in a much later update
Also, I checked the earliest version I have on the pc, it's 0.2.10 and 0.1.1a (I think I started with that one)
Unfortunately, 02.10 it not early enough because both dragon girls have their routes and 0.1.1a is too early because we only just met Haramunia. So now I can't check if it's true that Seinaru didn;t had a route bust still appeared