OP I'm so sorry to hear about your mother, alcoholism is a vicious, relentless condition.
Just to share my experience as a recovering alcoholic myself, I can honestly say that no matter how hard you try, how desperately you beg or how clear the damage your mother is doing to herself and others is for all around to see, your mother will only be able to get help if she wants to help herself.
I am in my mid-20s so was not in active alcoholism for as long as your mother but almost all alcoholics have the same brain mechanisms which enable them to continue to destroy themselves in the way they are. I started drinking when I was 14/15, it became destructive when I was 18 (daily drinking, secret drinking, passing out every night, drinking huge amounts etc), and I was in AA by the age of 22.
Alcoholism is so hard to wrap my head around, as the drinking starts off as enjoyable, "normal", justifiable to yourself. "Everyone does it", "it's normal to have a drink in the evenings" etc are just some of the things which alcoholics tell themselves which allows the alcoholism to creep further into their lives, until suddenly they're drinking more and more and they're so far into the grips of drinking it becomes almost impossible to escape. In the last couple of years before I got sober and when my drinking was at it's heaviest/most destructive, I despised drinking. Every morning I would wake up in a hazy, sweaty, headachey fog and be desperate to just have a day off drinking today. My job and relationship were at risk, as was my health, and I was absolutely desperate to stop drinking but every day, without fail, I drank myself into oblivion.
I only stopped drinking, went to AA and got sober because I was already desperate to stop drinking but the catalyst was my parents finding me. They'd heard a crash upstairs, ran up to my bedroom and found me collapsed, unconscious and bleeding on my bedroom floor. I still cannot remember what happened, I must have tripped and fell, or passed out and fell, but either way it brought to their attention just how awful my drinking in secret was. Before then, they had no idea I was drinking in my room all evening, but this made them stage a forceful intervention and I was so relieved to essentially have no choice over the matter.
However, if they'd tried to do this intervention before I was ready to stop drinking, I can say with certainty I would not have stopped, no matter how much they begged, cried, pleaded etc for me to get help. The desire for alcohol was so much stronger than any of that, I can't even explain the grip it has over someone.
Essentially what I am trying to say is that an alcoholic can only ever get better if they really, really want to get better and it is very hard for them to want to get better when the alcoholism is telling ever fiber in their being that all they really want/need is alcohol. As hard as it is, you need to try not to take it personally. It isn't a reflection on you or anything you've done, at AA I met some unbelievably intelligent, kind, honest people who became secretive liars who would betray and deceive anyone and anything in order to ensure they could keep drinking.
You have done all of the right things in order to help your mother but it does sound like she simply doesn't want to help herself (yet) and a large amount of people suffering from addiction are the same. All you can do now is support yourself. Al Anon is a group for relatives/loved ones of alcoholics where you can go to receive the support you need and speak to people in similar situations to your own.
Please don't blame yourself or hold any guilt at all, please believe me when I say there is only so much you can do but if an alcoholic wants to keep drinking, they will. All of the things they held dearly in life before the alcoholism crept in now sit in 2nd place behind the priority of drinking. Your mother may know how much harm she is doing, but again speaking from experience, this won't allow her to change. Focus on yourself, while allowing yourself to be there for your mother if/when she can accept help.