Nan
I had the same situation arise when an old friend wanted to come and stay with my husband and I. He is a big drinker and we told him that he could stay as long as he didn't drink. We made it clear that we did not want him drinking in other places and coming home to our house either. He understood and decided not to stay with us.
If your friend can't respect your boundaries then too bad. You have your health to consider.
Like Rowan said. It sounds like there are many places that she could potentially stay.
hope that helps.
Karen