
Can someone remind me who actually prepared the poison and why FL wanted to drink it?

Both of them got a different poison. Peneloppe prepared a poison "just in case" but didnt actually use it. The sister used her maid to put poison in her drink so shed look like a victim and put the blame on Peneloppe. But peneloppe saw the sisters cup was poisoned thanks to the necklace and decided to drink the poison so she wouldnt get accused

Spoiler and question
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.I know the prince loved her in the previous life, did the Mc ever find out that he actually loved her before???? If so, how?? I know the Mc will fall for him again, but I hate the misunderstanding hanging... (/TДT)/

To answer your question, i don't think that the main character ever finds out that he loved her. The reason being is that, theres no one else that remembers the previous time line so that means she would never find out that he love her.
I think this is one of the plots where she just falls in love with him in denial cos she thinks that he hated her, so she will distance herself but ends up in confusion. Then in the process of distancing herself, the crown prince will become interested in her and yeah they fall in love.
He better be kicked out of the room in the next chapter. (/TДT)/