I agree with others: you did the right thing. My kids are 7 and 12 yo and they know about alcoholims. I told them when RAH was in hospital with liver cirrhosis few months ago, and I believe that was the best thing I did for them. As an ACOA who never got her reality validated I know how important this is.
I believe educating your kids about alcoholims (in a age appropriate way) is the greatest thing you can do for them, as by having that kind of knowledge in future life, I believe they're more protected from becoming A's themselves.
Last night my 12 yo D asked me why does daddy goes to meetings all the time. So I explained it to her, that it is important for him to be constantly reminded of the danger of active alcoholism, and to meet with people who share his struggles, as alcoholism is adiction, same as drug adiction, and it is really hard for an adict to stay off the drug, as his mind and body craves it. And that doing the meetings is the best known thing to prevent him from drinking again. So daddy is doing it because he is trying the best he can. She said: wow, I dind't know that, but it makes so much sense.
I agree with people when they say alcoholism is a family disease, so I do believe it is important that the whole family is aware and involved in recovery, as they all can only benefit from it.
Aslo, it is possible that some kids can make fun of her, if she told them, but you'll be there to talk things through with her and teach her to know better. You are who you are, you did things you did, and your kids would learn about it sooner or later one way or the other. I think it is great you were honest with her, it was very respectful thing to do, and I'm sure she'll appreciate it more and more in the years to come.