IMO, I think Alonzo and LDJ were not making it a very comfortable situation for Tawni. They were smoking weed, and if she is the troubled teen that everyone says she is, I'm sure she would've toked with them, too. And no THC showed on her tox screen. Obviously she felt that if she had smoked with them, she would not be in control of herself or the situation, so she was probably freaking out from the get-go. But who am I to judge? Maybe she just didn't like getting high. Just trying to put myself in her shoes (or lack, thereof).
Think about it-- new to prostitution, going to a truck stop that's secluded in the middle of nowhere, being in a car one girl she allegedly met the evening before and a pimp. If they were hitting her and kidnapping her by not letting her out the vehicle, she probably said "screw it" and jumped out.
Panicking, especially when feeling trapped, will make you do things that seem irrational, but when your adrenaline is pumping you just want to escape the situation at any cost. In high school, my sister and a couple of her friends had gotten robbed in North Carolina, and were sexually and physically assaulted and one of her friends got shot in the back and died downstairs. They were trapped upstairs, and my sister's friend punched a top story window out to free them and they all jumped out.. an hour or so later they were at my house at 3 AM, soaked in blood, screaming at my mother to call the police.