Welcome to SR. Whether or not she is an alcoholic or not does not change the fact that her lifestyle is destructive to herself and others; and also that _you_ as a loving family member are left to cope with the chaos she creates. There is hope as many here will also share about.
What I learned here and in Al-Anon was to make my decisions about how I would respond based _only_ on the other person's actions. Addicts and alcholics are very good at making excuses and oftentimes the family members are far too quick to believe the lies. This is what happened to our family as well. We needed to learn more about this disease and find a better way to cope and respond to the problems that arose.
I highly recommend you try Al-Anon, you don't need to have a 'for certain diagnosis' about your daughter's alcoholism. She has a problem with alcohol and that is enough....but it is _you_ who need the support of others regardless the degree of her problem. Another thing that helped me alot was to attend open AA meetings. (by myself- not with my family member)
I hope you will continue to come here to this forum, there are so many great people here who will share their own similar stories.
Take a look at our sticky threads too- there's tons of good information and especially selected permanent threads to help you.