Responses
I fear the FL is just a bit too oblivious or blinded by revenge to think about the whole picture. I noticed it throughout the more recent chapters but she wasn't aware of what goes on in the dukedom as much as she had originally thought. She also isn't good at connecting the dots, though that might have also be due to her consistently working
It feels obvious that someone tried to poison the Duke, but they switched foods. He has reasons not to trust people he just met and she has reasons to hate him. This could be solved by simple communication. I predict she'll start falling for him and THEN she'll discover how she actually died. Also her plan is pretty selfish when she could just quit.