Forget any idea that alcoholics drink for a reason. The family look for a reason (bereavement, stress at work, divorce etc) and the alcoholic seizes upon any reason, but it's rubbish. Normal people may take a drink to calm their nerves, or after a tough day and so on, but they aren't alcoholics. Your daughter is addicted, but will be grateful for any excuse to make herself feel justified in drinking.
It does take a long time to 'get it'. The alcoholic is in denial and the worse the condition gets, the stronger the denial's grip. And she has no hope of getting better until she accepts that she is dependent, that she lives to drink. That she can work some days and then feel too bad to do so, doesn't prove much. She is probably drinking every day and can function with an amount of alcohol inside her; indeed, stone cold sober she might not be able to function at all; but now and again she has just a bit too much, and can't.
She has to go to her doctor and a test for liver function, a blood test. And it would help a lot if she goes to an open meeting of Alcoholics Anonymous (one that is for the curious, rather than a closed one for people who have long accepted that they are alcoholics and who are in recovery)