As a cook, best way was for EP to put tainted mushrooms in 1 gravy boat, Ive suggested this all along.
Evidence easily discarded;
Really simple to flush away the liquid evidence and keep her specialty Beef Wellington "perfect"
Then, make fresh gravy for herself and her kids separated in a different gravy boat.
Makes a lot of sense to me. IMO, likely served the poisoned gravy too, to make sure everyone intended for it received "a dose".
We really need to hear from the survivor.