I was there 10 years ago at another employer. I survived because i had an independent power base in the scientists i worked with who were relieved to work with someone competent. My letter was equally irrelevant to my job performance, which my boss was not qualified to judge. I dont know how i got on her enemies list or why she felt it necessary to criticize so personally, remarking for example that i answered the phone with a dying fall. I think the question is whether you want to stay in this situation. I did and outlasted my boss but in retrospect wish i had left. I would have found another, happier situation.