I think Mangum was out of it and probably wasn't even aware of Kim's 911 call or half of what went on inside or outside the lax house. Remember, she fell on her butt down the steps because she was out of it, and that event would have made her more out of it. I think Kim made the 911 call because she was mad at the boys because they either got some of their money back or she was insulted because they weren't satisfied with their physical appearance, be it due to race or age or just general atractiveness, and she played the race card via phone to bring the cops down on them, hoping to get some of them in trouble for being drunk and drinking under age. I think she (and Mangum) sat down the road in Kim's car and she watched while the cops tried to roust/raise the boys, and left when she saw they were gone or not answering. She didn't want any direct contact with the cops because of her warrant, and di her best to appear to be the good samaritan and blow them off at Kroger's while still getting rid of Mangum. The 911 call really doesn't have much to do with anything pertaining to the case except help pin the time line down somewhat.
I believe the trip to Kroger is part of the AV's police statement.