When does the most important part of a fetus form

An 80-year-old woman who had been a zoologist for most of her life suffered from alzheimer’s disease. due to changes in her brain chemistry caused by the disease, the woman often had false perceptions of objects. one day, a guest at the woman’s senior citizen home approached the woman while wearing a furry coat. the furry coat worn by the guest caused the woman to hallucinate and believe a lion was about to attack her. to protect herself, the woman hit the guest in the head with her cane. the guest sued the woman for battery. the applicable jurisdiction follows the "single-intent" rule for battery. what is the woman’s best defense