Like many here, in cases like this, where my assumption is guilt, I always like to try and come up a plausible opposite narrative of innocence too. It’s certainly tricky with what we have so far!
But perhaps something like:
The suspect is preparing beef wellington. Realises she under-bought on the button mushrooms, and has no time to go and buy more. No problem - she has those dried ones in the cupboard she bought at an Asian grocer a while back! Rehydrates them and adds to the mix.
Lunch is served.
Her guests, who are all significantly more elderly and lower BMI than her all succumb very quickly. She only suffers mild sickness - perhaps somehow related to those two factors (older people’s health and organs are generally less resilient; BMI may have some impact on toxin levels?) or she eats less of the wellington than them for some other reason (on a diet or similar).
The kids eat the leftovers with the mushrooms removed because they are, like me, grossed out by eating fungus in any form and insist on it all being scraped off.
Some time later when everyone is hospitalised the doctors report it is suspected mushroom poisoning. At this point she starts to doubt the provenance of the dried mushrooms she used. *Were* they the Asian grocer ones she’d had, or could these be ones they had foraged some time ago? Now she’s not so sure.
Kids ask along similar lines and Dad overhears and makes the documented “is that how you poisoned them?” comment. Suspect panics, as she says, and in her wild panic irrationally thinks that removing evidence of any accidental poison mushrooms from her home will somehow exonerate her. Dumps the dehydrator and sticks with the story as she thought it was, prior to the sicknesses - that she was just using up some dried mushrooms from the grocer’s. Because that, in her mind, was the version of events where she was ‘innocent’.
It’s sort of possible, but for me I struggle to come up with any narrative that doesn’t involve the remarkable coincidence of neither her nor her kids eating (much of) the poisoned shrooms. Unless age really is a protective factor in mushroom poisoning, which so far I’ve found no evidence to suggest.
I’d be interested to hear anyone else’s attempt at a reasonable narrative of innocence!