I've written "I hate you" in emails but haven't said that to her face. I know I don't mean it and she knows it too, so it's probably not hateful to her.

However, I did write something very "hurtful" to her, which I know is not hateful, but I did it out of anger, so maybe it WAS hateful. I emailed a list of all the things I knew about her that she told me over the first year or year and a half of therapy. Personal things. Writing them in a list and sending it to her crossed boundaries (even thought she had told me these things) and was hurtful/hateful. I apologized and still feel ashamed of that email.