Clues to Raven's secret were present, even before you start to get to know her.
When Gaius gives Micah a tutorial about caring for befriended monsters, he remarks that Micah has a way with monsters, just like Raven. Micah and Raven are both half-monster.
Think about the bachelorettes who do not have a blood relative in the game: Daria, Kuruna, Pia and Raven. All are half or non-human.
Raven is one of six characters with pointed ears and responds to the Strange Scent cologne. None of the others are human. Gaius and Zaid are dwarves, Kuruna and Ondorous are Univir and Daria is an elf.
Karina often waits at Micah's house for her requests, and even stays overnight for one. At first glance, it's odd that she'd make the effort to visit Micah's house, considering her passive personality. However, since her arc focuses on her difficult relationship with Hazel, it's not a stretch to think that she's intentionally avoiding her mother by waiting for Micah at his house.
Related to the above: Hazel mentions that Karina used to be a very active kid, but Karina also mentions Hazel didn't use to pay much attention to her, so Karina's lazy behavior could be seen as a way to rebel against her mother's Workaholic tendency and maybe to make her pay attention to her.
Colette hates milk. Make perfect since because she's a Big Eater and too much milk at one time can actually inhibit your digestive process. With how heartily she eats it would make sense that rather than hating the taste of it she just always drinks too much when it's served to her and can't eat afterwards.
Sofia's quirk of liking items that are essentially trash has a reason behind it: her family is so rich and she probably could probably get anything... Except said useless items, especially Rare Cans and Super Failed Dishes which are actually pretty rare.
