Stressed out

I'm new at this site. My mom has done drugs pretty much my whole life, mostly painkillers, and then started meth and drinking a couple years ago. She went to rehab like a year ago until she got kicked out the first day she started day treatment only for bringing a coffee cup full of vodka. She insists that drinking was "never really her problem" and acts like it's normal to drink straight vodka all day long and hide it in your closet. 

Anyways, I go to college about 3 hours away and don't live at home most of the time anymore. I was in my college town last week when my cousin's wife texted me that she was really concerned about my mom again and wished she could at least convince her to get a physical. My mom had "elevated liver enyzmes" like a year ago and hasn't been checked since then. I just feel so frustrated that she would ask me because honestly I feel so over dealing with it and like there's NOTHING I can do. I'm so sick of it.

I came home a few days ago and as soon as I got back my mom told me she had just gotten a DUI and wanted advice on what she should do. My best friend got a DUI a few months ago and with her I feel like I can be understanding but with my mom I just want to be like wow really?? She blew what my friend blew at 2am after a night out in the middle of the day. 

I feel like a brat because I should be helping my mom but I can't help but feeling irritable and resentful every time I'm around her. 

I just wanted to try posting here because I told one of my friends a little bit about what was going on and she was like "well she's your mom. you have the best chance of getting through to her than anyone" and I feel frustrated and like she doesn't understand at all how sick I am of dealing with stuff like this. My dad is also in another state right now and doesn't know about the DUI yet and she doesn't want me to tell him. I just don't know what to do anymore. I'm just frustrated.