Because at the time Kim was telling a "good Samaritan" story that she found Crystal wandering by the side of the road. The DPD let her go with that. Only later did they come to understand her deeper involvement in the evening.
Maybe the DPD didn't take Kim's name because they are familiar with the AV. They picked her up drunk, half dressed, and minus a six inch white shoe.
I think Kim wanted to get out of there because she knew she had warrants out for parole violation. The same reason she supposedly hid her number on the 911 call and asked the Kroger's guard to call later. I bet she beat it within seconds of the cops arrving at Kroger's...
If you recall she was immediately arrested following her later statement when to cops found out who she was.