There was absolutely emotional rage and you can see it in the number of stab wounds to Travis' body. That's rage right there. Your opinion of her motive and calculating is interesting, but does not match either the facts of the case, Demarte's diagnosis, or the disordered crime scene. She wasn't evaluating data points, she was in pure "if I can't have you, no one else will have you" jealous obsession and rage. Overkill is all about rage. Stabbing someone is personal. This was a rage killing, pure and simple.
Most people with BPD are more self-destructive than inclined to murder. Their partners suffer because they are emotionally volatile, contradictory, unpredictable, and with poor impulse control particularly with regard to self-destructive habits. I don't doubt Dr. DeMartes diagnosis, but I think Arias' actions arose more out of sociopathy than BPD. The facts of the case match a calculated intention to kill, as supported by the premeditation evidence. In light of her sociopathy, I would say she was not obsessed with Travis, she was obsessed with what he could do for her, how marrying him would benefit her. There is a subtle but important difference. Her mother cried in the interrogation room about how her daughter could act so normal and happy, and this behavior was immediately after the murder. That does not indicate any kind of deep emotional bond, however broken, it indicates the cold emotional isolation of a sociopath, in which only their own life and emotions are real and have any value. To posit obsession with Travis into that void would be to give Travis reality as a human being in her psyche that could not exist. He was a thing to be used by her, and when he was no longer viable, and had actually become dangerous, she eliminated him, and was as normal after as if she had just taken out the trash.