From what I've seen she always spawns for the same spot. Once you find it, if you get caught, just go to that area. She will be on patrol. Otherwise you'll have to look around.
When I found it, it was in two different places, one was near the train line, the other was in front of the restaurants on the left of the map, after that I didn't see it anymore.
She only spawns when you are wanted as long as you have hypnosis film available to use on her and a free space to store an hypnosis photo. So make sure to be well equipped. :)
