To find Crystal, you need to stay in the village when searching for Angelina. Once you go through that path up until gaining access to the map, go to left side of the Crystal Cave. Then, you'll see her.
Oh! I never thought people would draw fanart for my game! I'll add such feature in some way later ;)
That's a bug I couldn't catch. This side quest is supposed to appear only after you go through the main story where you will meet Charlotte.
Thanks for your support! Really glad to hear you love the game ;)