Maybe those 3-5 drinks were this size.
Maybe she was drinking dry martinis or Rob Roys or Harry Buffalo...
According to this link, a person weighing 140 lbs, who had 5 “rob roy” drinks over the course of 2 hours, would have a blood alcohol level of .26 (or .21 for the martinis)
http://www.ou.edu/oupd/bac.htm