Why should she be in trouble. She was teaching them history. It is historically documented that Mohammad had a 6 year old wife. It would be like telling the student Jared Fogle was a child molester.
Well, when a country makes laws that make it illegal to “disparage religions”, then the fact that you were only telling the truth is not a defense.
Now, I am still waiting for the first radical atheist to be charged with a crime for “disparaging Christianity”. They do it constantly, but I guess the prosecutors in these countries are trying to amass a real mountain of evidence before they bring those cases to court :)