Hello Dillpickle,
I am so sorry that you are unable to come to terms with your mothers death, I agree that a death like that can indeed be a PTSD. I do think its a good idea of your therapist that you write a letter to your mom, but maybe not a letter,maybe you are not ready to write a letter.Sometimes words, just single words can be a start. Just what you are thinking when you are remembering that awful experience. Acceptance is a very difficult thing to come to terms with. My mom died in 2002 and I couldnt stop crying for years and this time of year is so dreadfull as you know all to well. Then my brother died last year and I felt numb. I couldnt cry. Then a few months ago, it all came together like a stunami. Tell yourself its ok to cry, surrender to it. Remember if you wish to write the letter, you dont have to sit down and "write". Do it at your own pace. Dont rush it, There is no time limit on grief, and go easy on yourself because if you are thinking like me , I beat myself up about not getting on with things and coming to terms in a reasonable ammount of time. Also I would just like to add that you said that you didnt have a service for your mother? Well maybe you could think about having one in the New Year. It is never to late to celebrate your moms life. I think that it would help you as that is part of a missing link. I am sorry its a long post but I do wish you all the very best and you can pm me anytime if you feel like talking or want a distraction. Take care of yourself.