Especially because the "X Man" who was supposed to kill her as we saw in last season's trippy animation episode wasn't very obvious.
Wyman: Basically, when Walter was going through the Nanites.From that episode when she was in William's head, she said, "I know that's the man who's going to kill me." She had a feeling that when she was in William Bell's head, that there was a man and it manifested itself as a character in William Bell's head in the comic that they're experiencing and it had that emblem on it.
Then, ultimately, in this episode, you saw in the in the Nanites they had the emblem on it. When Walter recognized that that was William Bell's creation by that mark, because that was the mark that William used to mark things with. So really, in a sense, it was William Bell who killed Olivia. You could argue, saying when she came out of William Bell's head, she said, "That's the man who's going to kill me," it was actually William Bell.