Thanks Maryjan and Tromboneliness for your much appreciated responses. It was my therapist who suggested sending an email. I've been feeling waves of intense anxiety every time I hear the phone ring or text bell go off. The old ptsd startle-response is back full force.
Of course, an email might just make her call more.... this is so tricky. I'm amazed at the force inside me that wants to pick up the phone or answer the text msg in order to "get it over with" because "I can handle it" and "it's not a big deal." But, I know that my internal responses to her are still very much linked to the past and to trying to keep everything calm so that she didn't have a violent blow-up aimed at me or worse. And, also, linked to trying to do everything "right" so that she will finally see me as a real, live person with my own purpose for being alive.
The boundary is definitely set and I'm unwilling to return to old patterns. I will meditate on sending an email or just letting it be.