Because the true crime group were her online friends, and she was (I believe) setting up the story of how she was a keen forager who (worst case scenario, in her mind, if the authorities ever suspected her) had accidentally foraged death cap mushrooms and accidentally killed her relatives.
But she wasn't going to admit that off the bat, she was (I believe) waiting for them all to die so they could not contradict her story... The lie about the health problem she needed to discuss with the kids absent, the ovarian cancer diagnosis, all of that needed to die with them.
Then to her horror, the doctors were onto her mushrooms being the cause way too early, and she had to ad lib, and meanwhile hoped they all died before they could contradict her story...
She would have been better of trying to fake some of her invisible tears and breaking down at that point, and saying, Oh my god, maybe it was the mushrooms I foraged, but she was all in on the Asian grocer by then...