Looool it IS super funny when they evolve! But baby Pokรฉmon always feel much more natural in PMD settings (probably because most of them are just living about their life, and not hyper-trained to be combat veterans, and baby Pokemons are under appreciated!) (final evolutions all have such an intense aura! LOL!)
Speaking of evolution, Castle was always meant to be an Arcanine in my head, so this 'rendition' of him is actually a younger version of it (and him being an Hisuian was a decision on the spot, and I LOVE IT). He was much older in one of my stories, with his suave and confident side being more prominent. I would play an Arcanine version of him if I could, but I love this younger version so so much as well equally!!!
And yes, Clara evolving into Glaceon=instant brownie points with Castle!!! I suspect most of the characters probably wouldn't evolve for a very long while (or the entirety of this rp), but somehow I can easily see Clara being the earliest to evolve and having an existential/identity crisis before it/because of it!
I don't intend on having Clara evolve soon, like you're saying, but she is genetically predispositioned to evolve more readily than practically everyone else here, so I do agree that if anyone were to evolve this rp, it would probably be Clara. It also would 100% cause her to go into something of an identity crisis. Not only is her body changing, but her entire typing is changing! I suspect regardless of what she evolves into, there's going to be a sharp learning curve where she has to adapt to her new body and type, and all the little quirks that come with.
My top picks for her are Glaceon, Leafeon, Sylveon, and Umbreon, simply because those are the color schemes I don't mind the shiny versions of too much. I feel like Leafeon or Sylveon evolutions would be good for plot hooks, especially, but Glaceon would give her a bit of her own identity.... the choice is tough.