In your example, I would say, "We're NOT strangers." "no stranger" is used in a different context. She's no stranger to something = she's familiar with something, or she's had a lot of experience with something She's no stranger to hard work (=this is something that she does all the time). That TV show is no stranger to controversy. (=they have had their share of controversies over the years) He's no stranger to conflict (= this is something that he deals with frequently)