The Cook County State's Attorney joined us on "TMZ Live" for an interview Thursday -- hours after Illinois' Supreme Court overturned Jussie's conviction because he agreed to a plea deal two years earlier -- and, she says she's not surprised by the court's decision.

Foxx says she took criminal procedure during her first year of law school ... so she understands double jeopardy -- and knew immediately Jussie's conviction in 2021 would be overturned.

Jussie fulfilled his obligations -- 15 hours of community service and a forfeiture of $10k in bail money -- so, that was that in her mind ... until she says Dan Webb, the special prosecutor, felt the public pressure and decided to try Jussie again.

As for if she regrets not going for a steeper sentence instead of giving Jussie such a light sentence for his plea, Foxx points out Jussie was convicted of disorderly conduct for filing a false police report ... a low-level felony.

Kim says people convicted of this are generally offered diversion programs ... so, it wouldn't make sense to prosecute Jussie just to prove a point.

KF claims Jussie's celebrity status drove people into a frenzy about this case ... which is the only reason he was tried.

Foxx says she does feel vindicated that what she was saying proved to be correct -- that Jussie shouldn't have been tried after taking the plea. However, she adds she's sad it took years and millions of dollars for that conclusion to come.

We also asked Kim about the politicization of the legal system ... and, you have to hear her thoughts -- sounds like she thinks America's at a tipping point.

BTW ... Jussie's lawyer Nenye Uche talked to us earlier today -- and, much of what he says jibes with Foxx's responses. Just like Kim, he thinks courts need to push back and defend due process in the social media age.