I just started following this case and finished reading everything...here's my theory/thoughts...
I believe she probably did stop at the Shady Lady after she left work. I think she and some friends, probably the ones she was going to meet up with, were into drugs (using or selling). She gets their money and leaves to buy the drugs so they can party (or picks up from them to sell elsewhere, like the QT, for extra cash). They make plans to meet up after, and then she doesn't show--perhaps there weren't a ton of phone calls and texts even when she doesn't show because she does this often--it's hard to know without knowing her habits. I don't think the wikihow article on how to disappear is relevant--I look up random things like that all the time and fall into a dark rabbit hole of weirdness online when I can't sleep or am feeling down. I think she got pulled over, and was possibly nervous about the stop (especially if she had drugs on her that she was in process of delivering) and made up an excuse about getting gas, so the cop followed her to make sure she made it safely (cops do that sort of thing where I'm from). Worried the cops were on to her, or possibly just paranoid because she'd been busted before, she unplugged the GPS--possibly not realizing how it worked and what it tracked. She gets gas, or pretends to, and one of two things happened afterwards. One--the cop was not the good guy and he pulled her over again once away from the gas station (re: the 'OMG I got pulled over again' text) and was met with foul play then. Two--She proceeded to her drug deal and was met with foul play then. This would explain why she was going north when she was supposed to be staying further south--she had plans with drugs that no one wants to talk about. This would also explain why the insurance gadget was disabled. I'd be interested to see where her phone pinged later and the dashboard cam footage from the stop and afterwards.
I don't think the news would still be running stories and the family would be trying to organize searches and raise money if the police knew she was safe somewhere or gone on her own accord (I think there would have been a press release, or even them talking to her family and telling them what they think happened and why). I think they aren't searching because they know what happened to her and are trying to prove it. I can see them being really tight-lipped if they're investigating a fellow officer or, if like some said, she was a CI who they realize met with a terrible fate.
Depending on her call records, she could have been planning to do a drug deal at the first QT, but because of some reason (cops near there?) she couldn't, so they were going to meet at a different one. When she was pulled over, she had to make an excuse and used the 'low gas' excuse. Then she left and circled back around after the coast was clear to meet whoever she was meeting and they disabled the gps--not a stretch to think someone involved in illegal activities would know to check for devices.