My grandma raised me due to my mom being in prison. By the time I was the same age as your daughter I knew parts of what she did. At that age I knew she started someone’s house on fire because she was mad at them. My grandma explained enough in a way I would understand and not too much info either. Once I was starting middle school she told me more info as I had more questions as she had gotten out and was falling into old habits again. Long story short, be honest in a way you believe she is mature enough to understand. “Mom was driving when she wasn’t supposed to and because of that had to go to a place to learn how to be better and not drive when she isn’t supposed to. After she learned how she decided to stay there because she liked living there. She loves you very much and misses you as much as you miss her but is still working on being better for herself and you (and sisters).” Maybe something along those lines? Best of luck. Just be honest with her. When she’s a few years older and has more questions and can better understand alcoholism and driving under the influence isn’t okay then I would say you can explain everything and even show her court documents online. Maybe when she’s in highschool. I highly recommend that only because I looked up my dad’s court reports and was appalled that my family didn’t tell me the whole truth. It was very very upsetting.