Don't matter why they have a knife, if they show you the knife first, its just a threat, give em the wallet. If they want to stab you, for vengeance or what ever, you will probably not be aware of a knife until after the fact. Yet its a good assumption. Need some clarifcation here: Murder attempt? Really? How seriousely did he/sho want to kill her? Did she use a complex sert of knife defence moves to disable the attacker, or was she luckily just still alive after the attempt had ended?