I don’t think they can actually convict Croix for terrorism because the missile thing was an accident that I doubt can be traced back to her without Chariot speaking, and she also helped to stop it, having 8 witnesses on that.

Another one of her crimes would be putting students in mortal danger, especially Akko, but let’s be honest, no one is going to rat her out about that.

Now… The app she made to steal the magical energy out people’s emotions is another thing, but I doubt there’s actually a law against stealing magic. And even if it is, Croix’s probably pretty rich thanks to her inventions, so she can bail herself out or at least pay for a good lawyer, to get as little time in prison as possible.

The only thing she could really be convicted for without escape is causing damages to the school and utilizing her lab, and the school’s money, for building something she wasn’t supposed to. But even then I doubt Holbrooke will press charges, since she seems more than willing to take Croix back as a teacher. So… Yeah. I don’t think she’ll spend much time in jail. Maybe a few years, but definitely not her entire life.