Your instincts are right. Tiffany Hartley is lying. Either she killed him, faked his death, or is lying about why they were trolling Mexican waters to begin with and he got killed. But her story doesn’t add up and in her various interviews she trips herself up over and over. And first off, these Mexican pirates have historically approached people to rob them at gunpoint, but in her case they suddenly start shooting to kill from far away? and get a good kill shot on him but miss her repeatedly? Then she says they get close to her and let her go but later she is pursued by them again? She’s a liar and the more she blabs to the media the more the holes are discovered.
Tell that to the witness that saw her being chased back to the border with gunfire, and the fisherman who had a similar experience when he had drifted over to the Mexican side of the lake while in a fishing tournament and they started firing on him, and he gunned his fishing boat (like Jet Skis they are quite powerful and fast) and pulled away from them.