She was suspicious at the time and thought that this would be a brief excursion that somewhat stretches legality, like most of the extents she will go to expose the truth. The only thing that made this any different was A) she made the error of bringing Jason with her and B) the yacht was on the verge of leaving shore. She wasn't intentionally endangering Jason or anything. She just wanted to put some of the pieces to this lingering story together. That she won a Pulitzer is not tantamount to figuring out why she went; that Pulitzer was won under the notion that she no longer cared for Superman, an empty award considering she was writing "Why The World Needs Superman" at the film's end. It was just her journalistic instinct to investigate.
Anyways, it all worked out peachy. Had she not made the error of bringing Jason, that guard would have bashed her head in. Jason revealed his superpower of throwing pianos, and then all was right again with the world.