Hi Holly, I'm very sorry to hear about your friend, I didn't see this on Sunday otherwise I would had found time to post rather than leave you thinking no one cared.
I am a recovering alcoholic, I have a few (5ish?) years of largely sober time behind me but I have relapsed in that time so it's not entirely in the dim and distant past that I can't remember.
Alcohol twists the alcoholic's thinking, you don't say if she died because of alcoholic related health problems or that she took her own life either of which is entirely likey as suicide is common among drinkers who find themselves in the depths of despair, sadly.
I can't speak for your friend only for myself but there were a couple of times I was very very close to suicide, each time was when I had been in a relatively extended period of drinking, ie more than 24hrs non-stop (apart from when passed out). My thinking was so twisted that I couldn't see past the end of my nose figuratively speaking and couldn't see a way out. I couldn't recognise that there were people who loved me and who wanted me to be better. It made me entirely selfish and blind to outside of my bubble.
I'm very lucky that I managed to haul myself out again alive because sobriety has shown me that there is so much to live for which I simply couldn't see when drunk. It really isn't a nice place to be and I understand why some people don't find their way out.
I'm only guessing but I imagine your friend cut herself off from the world for two reasons, so that she could be left alone to drink in peace and because she felt ashamed.
I'm not sure that going into much detail about the grim details of how it feels to be in the grip of active alcoholism would be of much help to you, I fear it would make you feel worse about your friend instead of you remembering her as the friend you loved but please be assured that you couldn't have done anything to make her stop. I'm sure you were a lovely friend but any change would have to have come from her and it's very sad that she didn't get there. I hope you're ok.