there was no mention of any performance issue though was there?
so it wasn't affecting her ability to do her job.
she was very silly to get caught though - and being that obvious puts her professional image at risk.
quite a lot of professionals - teachers included - take class As at the weekend - and still do their job well on monday morning. The problem is 1) the law (one i disagree with, but its still there) 2) perception - taking coke may not make you a bad teacher any more than getting drunk on a friday night does - but knowledge of it does affect your work if it means parents are pissed off/ call your professionalism into question.
I expect the reason there was no convction was there was no physical proof other than her own admission - and convicting people that take drugs is a waste of police time.