If your book was a mystery, what was the mystery and how it was solved. Murder was the mystery. Serafina solved the case. The journals of the baroness were the key
Did anyone in the book do something you did not like? The baron killing his wife and daughter.
What motivates a given character’s actions? Serafina wants to find out, who killed the baroness. Her actions are strong. She doesn't do anything unethical.
Disclosure: I received a review copy of this book from the author.