In trying to complete this quest, I've come across a bug where I've managed to talk Ruanga into attending the party. However, I don't have the option to poison the captain, only to hand over the drinks which results in the default crew members dying. I do have the poison and discovered the journal, though had done that before ever speaking to Ruanga. My quest journal also reads as though she has refused to attend, which she initially did. I spoke to her again, and managed to convince her to attend. I do have a save going back before I spoke to her, but I've read elsewhere that given I've already picked up the poison (which was when I first visited Thirdborn), it will still be an issue?