Also, I think a huge point of emotion for a game like IM would be the sense of isolation. Humans are by nature social creatures. We take comfort & find strength in the presence of others, even if the presence is not physical. A friendly voice over a radio is in most cases, enough to make a person gain strength and hope that did not exist moments ago.
By having SARA be a friendly/anthropomorphic AI, the player will lose that sense of isolation as they will be aware that a benevolent, ever-present, and potentially near omni-potent presence is constantly with them & watching over them. In other words, they'll have that seem feeling that I presume fills people who believe that a god is actively watching over their every moment. They will be confident that nothing wrong can come their way, they will be emboldened by having that presence with them, and they will never feel alone or have true fear.
The player needs these elements. Lets think about what made the Running Man bots so unnerving. It was their cold, lifeless calculation. They showed no fear, made no discernable speech or other communicative noises, they shrugged off bullet hits, and they made a consistent, slow, but ever-closening line toward the player. You could shoot the head off one training bot to have the bot just behind step over the dead body and continue its way straight toward you with not even a millisecond's pause.
This cold, unfeeling calculation devoid of emotion is simply something we can not understand nor relate to. This element further separates the players from the bots/AI.
However, if SARA turns out to be not what we expect simply because she is too good at what she was designed to do (I, Robot [the book, thank you very much]) then I would be completely okay with that.