Factual error: A scene takes place in the Rome Casino. In Italy there are only 4 official casinos, none of them in Rome.
Factual error: A Blue1 flight is shown landing in London and a LAN Airlines flight is shown landing in Rome. Those airlines do not service London or Rome.
Answer: It's never fully explained in the movie, but it seems more likely that Rayna simply had a lot of enemies and people we're trying to kill her for various motives, but not to steal the nuke. For example, the guy who tried to poison her seems to do it out of spite for Rayna. The steward on the plane seems more intent on kidnapping Rayna to get what she's selling (although the pilot before dying says "Stan and I already sold it...", so he may not be after the bomb). Karen Walker, who was a double agent who sold Rayna the CIA names, is more likely trying to kill Susan to avoid being found out and not Rayna. Although if Karen was trying to kill Rayna, she may have already discovered the bomb's location, through various means.
Bishop73
Right, when in the basement, to make Susan believe him, Fine asks her "Did (or didn't) Karen try to kill you?" And Susan realises he had sniped Karen and her driver to save her from being killed by Karen.