One possibility is that she's feeling stressed by Fish either because of his mating overtures or from a growing conflict over territory. I think you are right to separate them as soon as possible. In addition to the aggression/injury potential, female turtles that have been with males tend to lay more eggs, which is stressful for both the turtle and the turtle keeper. On her own, she'll still lay, but will probably lay less.
It's possible Fish is going to lay sometime soon but her behavior doesn't sound so much like she's gravid as it sounds like she's either nervous or not feeling good. A female that's ready to lay loses her appetite and is frantic to get out of the tank because she wants to lay her eggs on dry land. Here's some info on the subject:
http://www.redearslider.com/reproduction.html
Does she show any other symptoms of illness - irritated eyes, poor appetite, breathing with her mouth open or yawning a lot, swimming lopsided?