This is a really tough question. Without knowing the whole story, I even hesitate to respond. So please take this only as some thoughts, not as “advice” about what to do.
You think the alcohol abuse is a way she copes with depression. I’m wondering if the depression is a result of the alcohol abuse. If so, the best thing she can do is quit drinking and drugging. Even if they are not the cause, these behaviors certainly aren’t helping her any.
I also wonder if continuing to be so helpful is really helpful any more. Maybe it’s another type of “enabling”? One way to move forward is to tell her that you are worried that your help is preventing her from getting the help she really needs. Yes, urge her to see someone for an evaluation. Remind her that an evaluation doesn’t obligate her to do anything. It only costs a couple of hours of her time. And often an evaluation leads to some good suggestions for steps toward a happier life. Also urge her to consider finding a chapter of AA to help her with her drinking problem.
Meanwhile, you might find it helpful to attend a meeting of Al-Anon, the organization that provides support and information to those who love someone whose drinking is out of control. You can locate a local chapter by searching on the internet.
Your friend is fortunate to have a friend like you. It’s difficult for you to admit that you just don’t know how to help her any more but that may be the best thing for you to acknowledge to her – and to yourself. There’s a limit to how much a person can care for someone who doesn’t care about herself. She — and you — need more support.
I wish you well.