One of my character's accidently kill's her neighbor's baby -- how could it happen? (have writer's block)?

While she was caring after the child one evening, while the parents were out. A long distant relative stops by, from out of town, unexpectedly (who doesn't know of her) see's her and freaks out. He starts yelling at her to put the baby down and get out, she tries to explain herself. The relative becomes very aggravated and ends up stabbing the baby by accident, realizing his mistake he takes off leaving the piece of wood ( or whatever type of object) in her hands. A neighbor hears the commotion, she comes running in, only to see her holding the bloodied piece of wood and the lifeless baby in her hands...