Your grandmother invites you to tea, but you're surprised When She Gives you a pistol and orders you to kill Your neighbour. What do you do?
Well, Granny makes cookies and I like cookies, so do what is necessary for the cookies to continue! First!
My granny wouldn't need me to kill anyone. She's pretty tough. I can imagine her killing the guy and burying him before jeopardy starts.
Hmm... I wouldn't do any of the options. I would sit granny down, speak calmly to her, and then get her some sort of help because, believe or not, my granny did not try to organize murders prior to this moment.
I would take my granny to a therapist and say, "Darling, you need to help. (;" + throw tea at her face to wake her up. But this is IF she did it. My granny lives 5 hours away from me so I doubt she would ask me to do that xD.
Pffft! My granny could never, ever be a serial killer! *tentatively picks up a cookie that may very possibly be poisoned*