I could come closer to believing this if she hadn't slit his throat from ear to ear, nearly beheading him, which clearly was totally unnecessary, took an immense amount of energy and strength, and could possibly even be perceived as ritualistic. Totally evil. That in itself was over the top, negating the theory that she wanted it done quickly and cleanly. I don't want to argue about it though so I'll let it rest at that, and it is JMO.
Most criminals would shudder at the thought of having to nearly decapitate a human being. It's difficult, gory and beyond the capability of most humans. Arias could have shot Travis while he slept. No mess and no danger. Why did she want him in the shower? She wanted to terrorize him, taunt him and then murder him. She absolutely wanted Travis to feel mental and physical pain. I don't care if the whole thing lasted one, two or three minutes. Travis was stabbed all over his body and then his throat was cut from ear to ear--to the point of decapitation. That must have agonizing and unbearable. Even ISIS beheadings are not as painful. She tortured Travis to death and does not regret it.
I wish the animal abuse evidence had come in. She was violent long before she got involved with Travis and PPL. She might not be the very worst person in the world but she is right up there as one of the worst. She richly deserves the death penalty.