Hello,
Thanks for writing to Health Care magic, I am Dr , Muhammad Ahmad , I have read your question closely, I understand your concern and will be helping you with your health related problem.
I am sorry for what you have gone through, this was really unfortunate what has happened, as the doctors have told your mother's brain was without
oxygen for 20 minutes or so, after after that she is not responding to all the tests she has done to see signs of life in her, it means that her brain couldn't bear the brunt of oxygen deficit. Brain can only survive about 8-10 minutes without oxygen , 20 minutes was too much for it's capacity.
In my opinion unfortunately her signs show brain death and she according to medical science has no chances to recover, last and final test which is done is EEG to see brain activity if even that is negative then it is advised to get the patient off ventilator and let her go in dignity.
I hope this answered your question, If you have more queries I am happy to answer you.
Regards.
Dr.Muhammad Ahmad