Is the death of an elderly person, following their consumption of sweets given to them by someone who knew of their illness and inability to refrain [from eating them], considered murder? If so, is it intentional, semi-intentional, or accidental?

The woman erred in her action, but the man is the one who transgressed against himself if he was of sound mind, because he directly consumed the food while knowing of the harm. Direct action overrides the ruling of causation.

So, if someone gives another person poison without the victim knowing, or mixes it with food and the person eats it unknowingly, then the giver is liable for qisas (retaliation in kind) if the poison usually causes death.

However, if the mature, sane eater knows about the poison, then there is no guarantee (liability) on the one who placed the poison, just as if a knife was presented to him and he used it to kill himself. If the eater is not legally responsible (a minor or insane), then the one who placed the poison is liable for him.