Hi Claire,
So sorry you are going through this. I was in a very similar situation with my mum - she died three years ago and reading your story (and everyone else's) brought all the feelings back. All I can do is agree with the advice everyone else has given - you need to look after yourself first, and let your mum be responsible for her own actions.
There's nothing you can do to stop her drinking, if she wants to she's going to do it regardless. Would also agree that if you can, leaving her to get on with things would be the best course of action. If you feel too guilty to do this, try and do something to make yourself feel better - for example, still visit her but only do it in the mornings when she's sober, do little things to manage the situation (like putting a load of washing on for her, tidy up a bit) but only do these things for YOU not for her. You are NOT responsible for the situation, she is.
My sister and I pretty much left my mum to her own devices in the end. She was determined to drink herself to death (she'd been given a terminal cancer diagnosis by this point, after years of alcoholism and heavy smoking), and it was squalid, horrific, distressing. We'd pop round every couple of weeks (no point phoning as she was always too drunk), sort out bills etc, change the bedding, that kind of thing. We both felt guilty we weren't doing more, but by this point we'd tried drying out clinics, doctors, hospitals, AA, AL-Anon, and nothing stopped her drinking so we gave up.
Your mum's alcoholism isn't your battle to fight, it's hers. It's easy for the rest of the family to make you feel guilty about not helping your mum - easier to do that than to actually help her themselves. It's not your problem.
Big hugs.
You can CAT me if you need to talk.