It is a natural response among those kinds of people when someone is pi$$ing them off, or they feel threatened.
Kim got scared, because she has a record, and if Mangum took out a warrant on her for hit, bruising etc. Kim would be in trouble.
If what Kim is saying is true.
....which brings up another point. Kim may not have associated Mangum's statement with an idea of her actually wanting the bruises, but now she's spinning it. At the time, Kim may have associated it with something she was doing to Mangum, such as taking her money and/or trying to dump her out of the car. So now she brings it up as though it was said in context of a plan by Mangum to cry rape and her statement that it chilled her to the bone and she intended to tell the authorities about it is embellishment that serves two purposes: 1). It associates the statement to a plan regarding the rape instead of to her own behavior toward Mangum (trying to dump her after possibly taking her money); and 2). Provides a means by which, because of 1)., she can insinuate her importance to the story even further while simultanously humanizing herself (chilled to the bone.tell authorities).
It may be true that Mangum said this, but I seriously doubt she said it in connection with an intention to cry rape or that Kim right then and there decided to tell authorities about it, and I certainly don't believe she was "chilled to the bone" unless it was in fear of Mangum's pimp.