Zanko, I couldn't agree with you more. Thank you for this valuable input!
Scenario I thought about (your question about what would make Tawni jump):
Perhaps Tawni associated with people who knew LDJ on a somewhat regular basis, and that's how she was "introduced" to it. Maybe Tawni had been turning tricks on her own, or had a different pimp she was working for (Phelps??). Anyway, whatever the case.. say after she got into this fight with her mother, and she ran away because that's what she did to cool off. She meets LDJ, and LDJ OR WW promises all of these good things for her, some work, money, food, shelter, whatever she needed. "You won't have to steal things anymore because you'll make so much money doing this you can have whatever you want." So she decides to try this out, but doesn't want to live on the streets or anything. So LDJ comes over, helps her pack her things, her mom tells her goodbye because she's used to this anyway. Alonzo is waiting outside for them, and LDJ makes sure Tawni is sitting in the middle. So, they go to Van Buren and maybe Tawni has frequented the area a lot and is comfortable there. So, in front of the car lot, maybe WW mentioned to them that he was going to take them somewhere else to turn a few tricks,perhaps even Tucson, and Tawni was not comfortable with this. So, they argue in front of the car lot. WW starts getting angry.. this girl is giving him a hard time about a place he knows can make some good money. So, he says whatever he had to say to get both Tawni and LDJ back in the car, and off they go to toward Eloy. Tawni starts panicking in the car. Telling WW to let her out so she can go back home. She's in way over her head now. She might be yelling and begging to just let her go. WW is starting to reach his boiling point, because Tawni is being "defiant" with him, so to show her who's boss, maybe he hit her. He might be screaming and yelling at her at this point, calling her names and making threats. Her alarm goes off, and she just wants to go back home, so she positioned herself in LDJ's lap, claiming if they don't stop she's going to jump out. Alonzo doesn't stop, and is throughly ticked off (I wish I knew what he was reaching for in the back at this point). Tawni continues to threaten to jump, and he probably doesn't care at this point. Maybe he's reaching in the back to say "good, take your crap with you too". And then it happens. I can see Tawni having a stubborn personality like that. After all, she was a tough girl. Says to herself that she can sustain a few broken bones and some road rash to get out of the situation.
Perhaps Alonzo covered his ass by saying "she wanted to be let because her boyfriend would beat her" to cover up any marks he could have left on her, so they could just assume "the boyfriend" did it?