I am not one of those who think a female teacher has sex with a student is no big deal. This situation is quite a bit different than almost all others. The age difference is very small and she likely never knew of the guy through school.
I don't think this situation is what the legislature had in mind when they passed the law she violated. Because of that, I would not vote to convict if I were on a jury.
That anyone thought anything wrong with this is just plain stupid. When I was 18 I was dating women a lot older than that!