In the movie "Body Heat", what is the true identity of Kathleen Turner's character?

In the 1981 erotic thriller "Body Heat", the true identity of Kathleen Turner's character is Mary Ann Simpson. In the movie, it is revealed that Mary Ann Simpson (Kathleen Turner) and Matty Tyler (Kim Zimmer) graduated from the same high school in Illinois.

After high school, Mary Ann Simpson gets involved in some bad things (criminal situations). So when she sets her sights on wealthy Edmund Walker (Richard Crenna), she knows that he will not marry her if he finds out about her past. She decides to adopt the identity of her high school classmate Matty Tyler. As Matty Tyler, she (Mary Ann) meets Edmund; they get married and she becomes Matty Tyler Walker. They move to an enjoyable waterfront estate in Pine Haven, FL.

All-in-all the film takes place in the sizzling-hot Florida town where Edmund and Matty live. Attorney Ned Racine (William Hurt) becomes dangerously involved with the sultry Matty Walker (Kathleen Turner). He will learn that her real character is Mary Ann Simpson. Together Ned and Mrs. Walker (Matty) will look for a way to get her wealthy, much-older husband out of the picture. Ned's knowledge of legal matters may allow both conspirators to escape unpunished. Matty Walker is however craftier and more self centered than anyone including Ned ever dreamed.