OP, I am so sorry for what you have been through. Your post has really resonated with me.
I had an ED from the age of 14 until I was in my early thirties. It was at a time when hospitalisation was much more common. I do not want to mention exact weight, but my weight dropped to just below the weight you mention whilst I was an inpatient on an acute psychiatric ward. I think I pulled through physically, simply because i was too weak to fight the interventions when they were applied. I was also sectioned several times
My mother was also criticised by her friends, including friends at church, for not taking a firmer hand with me. My brother was not criticised, nor was my father, only my mother. She ended up in hospital with hypermania and I think this was mainly the result of the stress of seeing me as I was and being unable to do anything at all to stop it. Believe me, she tried. Even when I left home (it was impossible for anyone to live with me without being affected by my behaviours) she was, on many occasions, my only support.
I did pull through, and went on to establish a career that I love, and I married and had two sons. I thought I had put my past behind me.
Then, my youngest son developed an ED. It was so similar to my old ED that I felt it absurd. For some time, I felt guilty because I could not 'stop' him, despite noticing some early signs. We have tried to get him help, but he does not meet the criteria for the ED services, so help comes through the mental health team
Yet, watching my son's life never take off due to this all consuming 'obsession' with food, weight, exercise, restriction, binging and purging, has been traumatic for me, but it has made me understand the absolute impotence of my mother's position. I have tired everything, absolutely everything, and still the ED remains. Just as she tried everything with me. There were also times when my mother and I would plead with the services to let me try to 'recover' at home. She did this because she really believed I could do it, and because psychiatric hospitals were - well let's just say - not very good places at that time.
When I began to recover, I recovered because something changed in me. It was an internal change.
In conclusion, OP, I really and truly believe that your mother did everything she could. I know I have not written this very well, but please feel free to ask any questions.