This discussion of the root problem is useful, but let's not let it become a red herring or distraction from the rest of the problem: I mean even if the stop happened and was legal, there is a real and valid problem in the way the trial occured, once she presented the proof of valid license and insurance, that should have been the end of it - including a reimbursement for expenses incurred.

I am curious about racial motivations and racial disparity though. It might be reasonable to think that the cop didn't pull over the people due to their race, as it was dark and I don't know if there was any way he could have seen that well. I wonder though if there is a way to find out a stops vs "run the license" ratio and if it indicates any racial biases. The run the license part should be gleanable from logs, but the number of stops part may be difficult - I don't know how those are recorded and how accurately they are recorded.