Good for you for going back to work and being willing to get help and stop drinking.
Is there an HR department where you work? When I had a breakdown I told them what had happened and they passed on selected information to my boss but nothing specific about my mental health history or anything. If you have to deal with your boss directly then I'd say that you had a breakdown (like you already told her) and that you're getting help, have support and are keen to get back into a routine.
My last boss was really good and let me do flexible hours for therapy etc.