I don't know.... I think if she planned to off herself,
she would not have gone through the trouble of dying her hair, lying about where she was going/making sure no one knew where she was, caring about what color car she was driving, filling gas cans so she wouldn't have to get gas in Mesa, and turning her cell phone off. I don't think she ever intended to kill herself, or stage something with the gun and that it was more of a back up weapon OR, she did just intend to shoot him, but her rage took over and she wanted to make the kill more personal.
I think she says things that she thinks will be more believable. Often you hear suicidal people claim that they aren't strong or brave enough to kill themselves (warped thinking, but that's another topic) and Jodi is BIG on taking cues from people who actually can feel and trying to act as if those are her emotions.
JMO, of course.