Hi Nephewaunt, my heart sank when I read your story because I went through the exact same thing with my sister. I said a lot of things to try and get her to stop, but after tons of failure and arguments my best approach ever was to tell her the following. "I know you drive drunk with the girls, whether you want to admit it or not. At this point I cannot control what situations you put yourself in, but I will do ANYTHING to make sure my nieces are ok. If you EVER put them in the car with you while you have been drinking please know I will not hesitate to call the cops." I told her this once as she was about to drive off, she was liiiivid, but after hearing what I said she let the girls out and ended up not driving because she was afraid I would call the cops.
I also warned her that if her behavior around my neices did not stop, I would also call social services. I had to call them as well.
Whatever conversation you have with her, please be sure to follow through on what you tell her! I went through a huge battle within myself and my family when I called social services, but at the end of the day, the kids safety is the ONLY thing that matters.
Be strong, good luck, stick to your guns, and have faith!!! :-)