Different stalkers would be if they had their own personalities, such as a more calculated one that either is better at cutting off the player by putting herself around the corner or just using cameras in some way (could count every time the player is spotted by a camera or is caught and just snap the player's neck once getting to five, for that extra bit of "she is just playing with you"), one that is less aggressive, is really good at getting behind the player but is very deadly if the player makes eye contact and maybe one that is more direct but is less likely to check lockers or other things that would be more smart.
I'm really interested in what you said with "multiple endings based on how the player interacted with the AI and the puzzles in the game".
Keep up the good work!