If she were mentally ill like Andrea Yates (i.e. not knowing what she did was wrong and verified as suffering from psychosis, which is a legal defense) that would be a mitigating factor. Arias knew right from wrong so there's goes that theory. She was able to plan and carry out an elaborate series of actions, all done to affect her murdering Travis. She drove to her "abuser" and there's no proof she was invited there and in fact she took great pains to hide the fact she was in AZ. There goes that theory.
Her only mitigators are no prior felonies, 1 adult victim, no others killed. And of those, AZ may only recognize the no prior felonies, not sure.