Penelope planned to drink the poison herself but then Yvonne was the one with the poison in her cup, Penelope knew that Yvonne was most likely plotting to make it seem like she wanted to harm Yvonne since she returned home. So she took the cup with poison and drank it with the intention on dying. I’m guessing she’s fed up with the game and wants to go home.
Read the chaps when they come out on asura scans. There’s a reason why they take the time to create good translations
Penny plans to drink her own poison after the party, she doesnt want to ruin the party that the Duke painstakingly arranged for her (she's really touched as to how he's been trying to be a father to her), so she decided to just poison herself when everything is over, and just quietly die.
Then comes Yvonne and Derrick at the party, so Derick announce Yvonne as the returned daughter that caused wtf to all the guests, so out of spite Penny just went with the flow and say "The real Daughter is back!" So Derrick (controlled by Yvonne) arranged to have the cups ready (which the maid controlled by Yvonne already put poison)
Again, to spite Derrick and Yvonne, Penny also declared about the return of the real daughter and with it both of them will drink the wine to celebrate. When the cups are presented to them, Penny noticed that when Yvonne's cup passed to her, the necklace from Vinter that can detect poison changed color (meaning the cup was poisoned), that's how Penny concluded that Yvonne's gonna poison herself to make Penny the villain. So Penny said immediately that their cup was switched and grabbed the cup from Yvonne, after talking to the audience Penny drank the cup and thus she got poisoned. In short, Yvonne planned to poison herself but Penny ruined her plans.
Also, the poison that Penny bought from Vinter isnt supposed to hurt, it's supposed to make the victim experience a painless death, just like falling asleep. Yvonne's poison on the other hand is supposed to make the victim suffer and vomit blood nonstop (it doesnt matter to Yvonne because she can't feel pain anyway).
Omg thank u yall this helped me out a lot, im gonna wait for better translations to come out before reading on lol
Genuinely I do not understand who poisoned who and what their intentions were? Or has it not actually been revealed yet? These chapters r so badly translated I cannot