Glad you were able to talk to S16 before anything else happened. Also glad the Principal listened to you. Teachers are pretty skiddish these days, and they have a right to be, but it does make it hard when the student doesn't utter what they think he did.
It is probably useless to say this, but if you could reach the place that you do not feel that it's necessary to try to explain everything, or to even give your W an "answer" to whatever she says......you would discover there are less arguments and you'll be more at peace.
It seems to be a common theme amoung the LBH's and I can understand it, but it doesn't change her. I'll even go a bit farther and add this....even if you think she is "listening" to the message you're trying to give her....I don't think she really hears....not from you. She may hear somebody else say the same words and respond better.....but not you. You will truly be much more affective if you can learn to say less and let what she says run off your back....as long as what she says is not disrespectful to you.
It is not about what you feel should work in your M. It is about doing the work that gets the right results. Do what works!