According to wiki:
The film's female lead has been discussed by psychiatrists and film experts, and has been used as a film illustration for the condition borderline personality disorder.<9> The character displays the behaviors of impulsivity, emotional lability, fear of abandonment, idealization/devaluation and self-mutilation consistent with the diagnosis, although generally aggression to the self rather than others is a more usual feature in borderline personality disorder.<10>
As referenced in Orit Kamirs' Every Breath You Take: Stalking Narratives and the Law, "Glenn Close's character Alex is quite deliberately made to be an erotomaniac. Gelder reports that Glenn Close 'consulted three separate shrinks for an inner profile of her character, who is meant to be suffering from a form of obsessive condition known as
de Clérambault's syndrome' (Gelder 1990, 93 - 94)".<11>
^ Robinson, David J. (1999). The Field Guide to Personality Disorders. Rapid Psychler Press. pp. 113. ISBN 0-9680324-6-X.
^ Wedding D, Boyd MA, Niemiec RM (2005). Movies and Mental Illness: Using Films to Understand Psychopathology. Cambridge, MA: Hogrefe. p. 59. ISBN 0-88937-292-6.
^ Kamir, Orit (2001). Every Breath You Take: Stalking Narratives and the Law. University of Michigan Press. pp. 256. ISBN 978-0472110896.
http://en.wikipedia.org/wiki/Fatal_Attraction
Probably a host of defense mechanisms (projection, denial, distortion, passive aggression, etc.) at work as well. We all have them. She truly saw herself as the victim. Of course, the Dan character was not blameless either as it takes two to cheat. Another psychological thriller I especially liked was Single White Female.