Long story short... my mother-in-law, (who was a well rounded, middle class citizen), was addicted to crystal meth for about four years. She has been "clean" for about two years, but in the last month or two began drinking alcohol. It's not that she has done it in excess, (that I know of ) but the fact that she has done it at all worries me that it could lead to something else. Do I have reason to be concerned?. this is my child's grandmother

I would be, when it comes to addicts, all drugs (alcohol included) are considered "GateWay" drugs. They shouldn't do anything at all if they are a recovering addict. Clean is clean nothing else. So keep an eye on her. Good luck to you and your family.