I recently rewatched If Then Else and they say that Samaritan did not have access to the Stock Exchange feeds, and Root and Finch specifically hacked into the feeds so the Machine had access, but Samaritan didn't. Which also explains why Samaritan is still not onto Fusco.

It was filmed as episode 7 because of scheduling reasons, but was always intended to air as episode 4.

Yeah, this could be wrong, but my impression was that Shaw was at least partially controlling the behavior of the other characters. Like Samaritan was guiding the context and scenarios but Shaw was filling in the details, and this was kind of in part her imagining of what would happen.