IMO it became a perfect storm in Jodi's mind. The move back to Yreka, the dead end town, dead end job, small room at grandmas, a repossessed Infinity, a blown up BMW and her obsession was 1,000 miles away. She can't drive by his house to see who is there. She can't just drop in with some excuse just to see him. All she can do is stalk him via hacking his email, his Facebook or MySpace. It's not fair. He has a nice home, friends, car, job and he's looking for a wife. The wife will not be her, she is the late night phone sex call girl-not the girl he will share his life and lifestyle with. It's not fair. He is moving on. She can't. Something has to change for her to move on.
Then the May 26 fight. He makes clear that he knows she slashed his tires, twice. She hacked his Facebook He berates her. He admits he is addicted to her sexually and hates himself for not being stronger. She realizes that even if he has sex with her he actually feels disgusted by being with her.
So even if she moves on...she's put in almost two years of investing in being a PPL member, of being a Mormon. She likes the fact that Mormon men are marriage minded. She wants a successful man to marry her. Get her out of grandmas extra room, out of Yreka, away from the Purple Plum. She wants a house, a car. She sees a Mormon man as the quickest way. There are possibilities in PPL as well (hello Ryan). If she established a relationship and it became serious, Travis has a good chance of hearing about it. So, six months of building a relationship (for example) could be ruined by a phone call from Travis "hey dude, be careful...let me tell you just some of what I went through with her"...she doesn't have that kind of time.
It becomes clear to her. For Jodi to move on, Travis has to die. That way he cannot ruin her future love life and she gets rid of her obsession. She won't have to check up on him anymore. She won't feel bad anymore. And he won't be calling her any more names. She won't be the girl good enough to call at 2am for phone sex but not good enough to marry anymore.
So she steals grandpas gun and plans a road trip...