YES^^^^----I think that's what she expected. That's what happened with Simon's recent mystery illness.
I think she put too much Death Cap powder into the meals. If she had backed off a little, it probably would have gone more the way you described. They'd be very sick like with bad stomach bug, feel weak and stay home, start feeling a little better, but then their liver would shut down. That's how Death Caps sometimes work. But I think the fine powder as a loading mechanism was very lethal.
The powdered Death Cap toxins went immediately into the blood stream and the digestive tract and then onto the liver, very quickly. She overamped the poisons, imo.
Yes, we cannot possibly try to 'figure out' what she was thinking. It was not a normal, rational thought process.
One thing she did tell the truth about---she did get panicky because she thought they were suspecting her. So she clumsily tipped the dehydrator and then lied about it repeatedly.
I think she was engrossed by vengeance. Starting with her resentment and anger towards her own mother and thus became estranged from her family. She tried to join a new family, who were loving and accepting of her--at first, because she pretended to be like them and have the same beliefs and philosophies. She shared some of her wealth with her new family, helped with their family business and with the church tasks. But secretly she began to think they were not as smart as her, not as educated or sophisticated as she was.
And her arrogance and resentment grew. Eventually she was consumed by that darkness, imo.