Maybe she kept asking it because she knew the boys wanted their money back - some of them did, anyway - and since Mangum was falling apart and didn't have all of her stuff and she (Kim) was mad at the boys, she wanted to know that they didn't take Mangum's money back.
Or she ripped Mangum off. But I don't see where advancing a complaint call against the boys that she wasn't going to show up for - maybe watched from down the street - would give her cover for ripping Mangum off. The only person she would have to worry about is Mangum's pimp, and he isn't going to be privy to the 911 call. I think the 911 call was unrelated and just done for spite because she was mad.
The one thing that I cannot figure out is that first phone call.
You would have thought a call like that would have been make by the fake accuser.