Well, you can't say anything to someone like that, and it's useless to try. All you can do is accept that your housemate doesn't get it and most likely never will. Following that, you simply ignore her.
Many of us deal with some version of this, by the way. Seems there's always a friend or family member who doesn't get it in some way.
In my case, because I was "functional" (at least as far as the outside world knew) I had people telling me that I wasn't addicted or that my drinking wasn't that bad (meanwhile I had been drinking myself into a stupor daily for 25 years, since the age of 13!). It's kind of amazing to listen to stuff like this when you know darn well that your life hangs in the balance, isn't it?
But no matter how ridiculous or offensive it is, it's merely someone else's limited viewpoint and needn't have any impact on us. Hit that mental "ignore" button!