Why did she have to dump her? Why not take her home?
Unlike members of the media, strippers don't harbor any illusions about the chararcter of other strippers. No way she wanted CM in her home.
Now, if you mean Mangum's home, I suppose since she was passed out and her purse was back at the house on Buchanon, Roberts had no way of knowing Mangum's address.
That's one of the reasons why I think Roberts may have drugged her while they were in the bathroom having money shoved under the door to them, and may have staged the dispute in the first place - to rip Mangum off by getting her out of there long before her ride showed up. Obviously, Roberts wouldn't take her home and run the risk of somebody Mangum knows well, such as a family member or even her BF, seeing Roberts push or pull Mangum out of the car. Roberts couldn't just shove her out in front of Mangum's house and she wouldn't have wanted to ask for help getting her out at that location and at that time, because it would have revealed who brought her home and when which then explains what heppened to Mangum's money, as well as revealing the fact that they left the dance engagement much earlier than planned. I'm sure Roberts knows that would look damn suspicious to Mangum's pimp who would be wanting his money!
Of course, the other explanation is that Mangum was just too out of it to give Roberts her address.
So, it's hard to say why she didn't just take Mangum home.