She doesn't live in a cave. She lives in the Eidolon fairy-city. There are buildings and human-shaped Eidolons with clothes and culture and everything.
She has a line that says "I think my body grew a little", suggesting that she hadn't noticed the change (or maybe she lost track of time).
There was also an epilogue quest in the GBA version where she gets de-powered, and is turned back into a little girl.
I dunno, I always found it harder to believe she spent something like ten years in a cave and somehow ended up a perfectly groomed knockout instead of Female Gau.
I'm not sure what the point of this is? Just an ad for the novel, I guess? It's not coherent enough within its 3-minute timeframe to be effective storytelling on its own, and it's not really visually impressive outside of some very brief effects to be able to appreciated as a spectacle. Whatever.
Actually just the one (well, and the in-betweeners); Kim solo KAed the episode.
Are you trying to kill the two animators?