When is it acceptable to say to doctors – Do Not Resuscitate – My serious alcoholiclic mother?

My mum has been an alcoholic for at least 18 years, she has COPD, liver disease, kidney disease, serious asthma and cannot breath unisted. I found my mum at 4.30 am this morning face down on the floor. she was brought back to life by ambulance crews. The doctors have told me, she will never b able to leave hospital due to all the machinery keeping her alive. I don't want her to go, but there is no dignity in dying several times and being in pain throughout.