IMO this is the ghist of the defense- implication is that she inadvertently introduced death caps accidentally foraged at a previous date into the meal unbeknownst to her.
- she then vomits up her meal AND/OR as she is adding dried mushrooms randomly from multiple tuppers, she just happens not to get dosed.
- she may have accidently foraged death's cap mushrooms, in spite of being quite knowledgeable about safe vs poisonous mushrooms
- unlike the other mushrooms she foraged, she didn't test or try them
- in spite of constantly adding/sneaking mushrooms into the family's food, the death caps never got into their food
- when making the special recipe, she decided to get even more complicated and make separate and distinct pastries for each guest.
-when making the special recipe, which requires mixing and cooking all the mushrooms together, she never tasted it before constructing the separate pastries.
- She hasn't admitted that she made one recipe of mushrooms to serve to her guests, and a different, non-mushroom recipe to serve to herself and children, although that is what must have happened to completely avoid any toxins.
JMO