Having some time to reflect on it, I think Sara's green tea rice element in the bento box must have been truly awful. I obviously cannot prove this, but I think Tom had every intention of passing her through Last Chance Kitchen - why else were they caught so flat footed on that quickfire meant for 6? By putting Brooke in, they altered the competition so much that they could not confer a reward for winning the quickfire. I think they fully expected 6 and had to pivot. I think - especially at this late stage - Tom would only put a LCK contestant back in the game if he thought they were capable of winning the whole thing. Otherwise, what is the point? I think Tom knew Byron had reached his ceiling and, while better than Maria and Jamie, was still a cut below Shota, Gabe, Dawn, (and Sara). I think it was set up for Sara to get back in, but her tea rice thing was so terrible that Tom felt the integrity of the competition would be compromised if he passed her through. I think if Sara was arguably close to Byron, it could be fudged. But if Byron made no obvious flaws and Sara's rice was terrible (especially if the eliminated chefs taste the food off camera), Tom had no choice.
Sara was never going to win because of the exact quality that reared its head with the tea rice - quirky and eclectic is refreshing and has a high ceiling, so long as it works. It is a high wire act, and when it fails it tends to fail spectacularly. She was bound to have a high profile fail. It's just a bummer it had to happen before the final 4.