You can get back her if you search for the forest in abandoned town, the prison in arc city and in transilvania ( that idk but someone said).
Idk what of you mean by the question of Cassie but you can date her, do things each other and if you capture a thief you can do more events with her.
If you summon the fairies in the forest you can give them things like fish, milk, repels , etc. But if failed 3 times in the offer or just don't give anything they just punish you.
PSDT: Idk if I have grammatical errors too. But I hope this info help you.