Your perception of the role Lisa played in turning Jodi against Travis is something I hadn't considered before and I think it's spot on. In effect, Travis became 'useless' to her, and reminded her of her inadequacy.
Travis' feelings for Lisa would have been a huge embarrassment for her, and a source of anger towards Travis.
I'm not sure if her motivation to kill Travis stops there or continues to the threat he posed to her reputation, which was my sole theory before, but killing him would be a way to put an end to both problems, so to speak.
Reputation wise, if she is still telling people or leading people to believe she's going to marry Travis, etc, and so on, anything he'd do with another woman is going to puncture that fantasy and make her look bad. Know what I mean.
I think her father said how upset and embarrassed Jodi was that her fiance was on that couch with another woman. And that struck me as odd about the fiance reference. Then, Travis asks Jodi in February or March, I think, where that ring was. I couldn't help but wonder
when the ring went missing. If it was a ring from Deanna or the linda time period, who knows when Jodi could have stolen it and how long she'd had it before Travis figured out it was gone?
I had the thought that she was wearing that thing when she was in Yreka at Christmas, proving she was engaged! Yikes!
She claims not to know about Lisa until sometime in March or April, I think, but her father said that happened in the fall, and it was in the fall that Jodi started feeling suicidal. It was in the fall and early winter that his tires at slashed.
I recall she said that when she found out about these "texts with other women" in the summer, she didn't say anything because of their impending new york trip. I'm thinking she didn't say anything about knowing about while she was living in mesa. She had no conversation with Travis about seeing him and Lisa on that couch until probably much later than she claims. She makes such a show on the stand of the fact that she didn't know about Lisa. Can't be true. She said in her manifesto that she didn't know where Travis had been when his tires were slashed. I have to go back over the texts and journals to disprove her on that, and it's probably in there that she did know.
So back from my ponderings to what you are saying. She knew about his qualification for Cancun. If she was telling her family that he was probably taking her, and they didn't see her going, she'd look real stupid. She'd also look real stupid if she told her family he was coming to visit and he never showed up. She might have been under pressure from what she'd been telling friends and family in Yreka to make it look real. I don't know. I'm just randomly throwing it out there. Do we know what she told people in her circle about it? I can't recall.
Oh, and random, off topic. She texted Travis about how she saw his roommate go in the office and log onto the computer. Then log off. She said in her manifesto that when she wa in Travis' gmail, his friends could see him as "logged on." I believe that's the real reason she randomly told Travis that his roommate was on his computer. It was to give an excuse as to why there was a log on for whatever she was doing. I do not understand why he let that girl clean his house and have access to his stuff!