You assume that, if she actually did kill him, she did it there. But, OTOH, if she instead went there as a cover story.... One can explain the blood on the life vest by the simple expedient of putting his body in the back of the truck.
I'm not ready to call her a liar, but there really are things that sound strange about her story ... e.g., she describes him flipping forward over the handlebars after being shot in the front of the head. And I seem to recall her saying that she had to turn him over to notice that he had been shot in the head, as if the bullet had not gone all the way through (as one might expect it to do). Those sorts of errors could be explained by stress ... but they do sound like errors.