A couple of things. I am familiar with the fascination that sociopaths have for movies. That, combined with an obsessive-compulsive fascination to duplicate exactly, combined with a tendency to seek feminine power through magical thinking (witchcraft, Law of Attraction, etc)... I am thinking that there may have been a desire to duplicate the Psycho shower scene, for starters, as a ritual, a death that Travis might have told Jodi was the worst way to die.
The next element, the slit throat, is the way to guarantee salvation for Travis because, according to olde-tyme Mormon religion, this is a way for a man to "pay" for his sin himself because his sin is "beyond" the Atonement. You can believe she just slit his throat to shut him up, but considering the latest info on "sawing", why didn't she just shoot him to shut him up? Who would choose this grisley tendon-cutting challenge rather than get the gun?
Lastly, she shoots him in the head EXACTLY as he described when he was sitting on the couch in the foyer of the hotel, when Jodi had her head in his lap.
I don't believe these are coincidences. I think this demented vicious woman wanted to psychologically punish Travis and I believe she is into symbolism. This is one of the reasons she had sex with him before killing him, so she could "claim" him as his wife in the hereafter.
SPECULATION: All of this is because I believe she planned to have him sealed to her in marriage after his death by proving they were having an affair (photos) just like the Mormons have sealed celebrities to their mistresses. Eisenhower to his secretary, etc.