Here's a quote of Agrippina's story:
"When it seemed the old man wouldn’t die quickly enough Agrippina sent in a slave with a feather to induce vomiting, claiming it would cure him. Of course, vomiting might in fact have helped Claudius if the feather hadn’t been dipped in yet more poison."
Full story and 4 other strange ways, featuring Ruth Snyder, Pamela Smart, Larissa Schuster and Clara Harris (+ PodCast!) in:
5 Strange Ways Wives have Killed Their Husbands - WeirdWorm