Hi berrygirl, and welcome!
Good for you for going to Alanon. I want to echo what Cyranoak said, Alanon saved my life, too.
As for Alateen, my younger daughter started when she was 12. Now, a year later, she really enjoys the meetings along with my older daughter. Sometimes the 3 of us sit at the dinner table and we can talk "program language" about how to deal with challenging people/situations in our lives. They have come to realize that their Dad is just one of those people/circumstances, and that they have a solid Alanon/Alateen recovery family where they can safely talk about what those challenges are like for them and gain insight, experience, strength and hope.
That being said, if your daughter is willing to talk with a counselor I think that's great, too. My kids have been seeing a counselor since early this year and it has helped, but the meetings provide something different which has also helped tremendously. And keep in mind that at Alateen your daughter may hear some pretty difficult stories about what other kids are living with, too. That was a bit of a shock for my kids but it also helped them to have perspective, and in our case that was incredibly powerful for them. But since your daughter is not quite a teenager you might want to keep that in mind.
As for your husband's plans to leave, my thoughts and empathy are with you on that. All I can say is that one of the things that I have learned, thanks to Alanon is that this is absolutely true: "Let go, or be dragged." And that no matter what your husband does, you are okay and you are NOT alone. We get it.
Keep coming back here, it helps more than I can say.
Again, welcome!
posie