Usually contracts are written so that if you do something which damages your credibility as a teacher, they can fire or suspend you or whatever. Busted for drunk driving, for example. Hey, it can happen. If it happens once to a teacher with 20 years experience and an excellent track record, they'll probably be fine. If it happens repeatedly, or to someone who hasn't earned their tenure yet, they might point out that it is illegal and use that.
Here, we've got something she did years ago, but not that long ago (2009), which was legal. As I said, she still has the same credentials she had before, and even has a few years experience now and so is presumably a better teacher. But it comes down to her contract, and I suppose how good of a lawyer she can get. I agree that it would be a distraction in the classroom, but the school board blew the lid on it in the first place. They heard a rumor, found out it was true, and canned her, claiming that they're acting proactively or something.
Her career is over. Any school district she applies to now will look at her resumé and see that she was dismissed in the middle of a school year and ask why, and she'll have to tell them something. Because of this experience, she'll probably figure it's best to come clean up front, and that will mean she won't be hired except maybe by the most desparate school districts. Her current school district could at least have kept their mouths shut for another two months and let her finish out the year, infinitely increasing her chances of getting a job elsewhere. But they didn't just fire her; they ended her career. They didn't have to do that.