Isaiah died from an allergic reaction. Someone induced the allergic reaction.

When did they have the opportunity to do so? Read the Crime Scene Report carefully.

Someone induced the allergic reaction during a game of King's Cup.

Someone spiked the wine during King's Cup. Who couldn't have done this?

During a game of King's Cup, one of Isaiah's friends spiked the wine with peanut oil. We know the wine was spiked during the game because the bottle was opened at the start of the game. Isaiah drank the wine and went into anaphylactic shock.

Elise couldn't have spiked the wine. According to the rules of King's Cup, she wasn't allowed to do anything for herself (like stand up or pour something in the wine).

Elise can be eliminated, and the pieces of evidence that support eliminating her are: the King's Cup Rules, the Crime Scene Report, and the Toxicology Report.