I got the impression that it was Danniella. The video/podcast in the OP suggests that as well. At least in the first clip.
The second female voice does sound different / not as intoxicated. But who could it possibly be? Danniella had been following him since they left the bar, right? The other female friend (Mallory?) who was with them made it to the other bar. Would Denson have called someone? If so, why? He didn't know Danniella was going to flash her lights at him to pull over. And even if he had planned on pulling over there all along, why call another person? And then, Denson goes back to the bar to get Danniella's phone. Where was she? He says he thought she was following him back. Would this second person have driven her somewhere to "hold her for him" until he returned? Seems really strange.
There may have also been another vehicle. Podcast said they couldn't tell if it was the same vehicle returning, or if it was an entirely new vehicle. Is it possible that Danniella followed a possible third vehicle by mistake?
I know the video was dark, but was it SO dark and poor quality that you wouldn't have been able to see if someone got out of the vehicle?
Okay, nevermind. This is supposedly the "surveillance" video? I don't know if the quality is this terrible because they're filming the computer screen, or if it's this terrible overall...