I am a little worried that your strenuous protestations almost seem as out of character as your writing/sending the email. The investigator/lawyer's elephant remark made some sense to me relative to that. If there's an "innocent" mistake made while you are on Ambien, that would be "all" there would be and you would conceivably be confused/puzzled at the uproar made. But you have a very detailed "counter-attack" happening which belies your innocence?

I kind of doubt we can write and send emails that we don't have in us. Yes, if you were wholly awake you would not think of putting what you thought into words and sending it to this woman, it would get you in trouble! But here you are in trouble because you did write and send such an email and though you apologized, you now have this woman taking it out on you. Instead of trying to appease her though, calm her and being upset at what she is doing, you are fighting her fire with your own, at the same time you are trying to defend yourself from the formal upshot of having written the email. It doesn't come off cleanly to me.

Is the letter from your psychiatrist about the Ambien causing you to lose inhibition or about the damage this other woman has caused by being in your face and trying to wreck you? If your "friends" can be turned by this woman's opinions and ugly words, they do not sound like very good friends? I'd leave my reputation in my better, longer-standing, experience with ongoing relationships hands and concentrate on clearing the official damage caused by sending the email.