Spoiler for trying againJust hope B-kun doesn't kiss Violet!
B-kun is already assuming any of the partners would have to have:
1) entered the kitchen, administered the poison, and left
2) re-entered the kitchen later, observed and edited the carved letter, removed the poison, and left.
In any case, no poison will be found in the kitchen.
If Violet is the killer, there are two scenarios:
A) First scenario, followed by
3) re-entered the kitchen later still and "discovered the body",
B) 1) followed by
2) re-entered the kitchen later, observed and edited the carved letter and "discovered the body"
If this is true, the poison is still in the kitchen.
UNLESS in 1) she kissed her daddy (having put on poison lipstick to which she has the antidote or a protective device), left and removed the lipstick.
In all of these scenarios but the last, the killer, upon seeing the carved letter, could have simply removed the sirloin along with the poison.
Only in the last scenario, when Violet returns only once, is it necessary to doctor the sirloin before "discovering the body".
I think the biggest clues here are the wilted lettuce, the grey meat, and a towel. Why a towel?