Greg Lynn's story was plausible. Unlikely, but plausible.
We haven't heard Erin Patterson's police interview yet, but I think she's going to have a tough time explaining how she accidentally attended these two exact locations that death caps had been reported growing, accidentally picked them, and then accidentally fed them to her inlaws.
Edit - I'm also keen to hear how she accidentally cured herself of ovarian cancer of the elbow.
The thing with your question, "how is she going to explain how she accidentally picked death cap mushrooms and fed them to her guests" , is that it is not what the jury is being asked.
That's not for her to explain.