Okay - you really could tell her to back off and that she does not know what she is talking about and to leave it alone. She might not do it, but you do get to tell her those things and it is okay to do so. The therapist can handle a client arguing with them and clients can learn that arguing with someone like a therapist will not end in disaster. I doubt she will fire you for emailing. She might not read it or she might want to talk about not emailing, but firing is probably a bit far. And since you have already sent the email, try not to beat yourself up over it. It is done now and you cannot un-email. So accept that you did what you did as an attempt to alleviate pain (not a bad thing in and of itself) and go forward. Making yourself feel worse is not going to help.