That's a good question. I will partially agree with Big Pappy on that you need to introduce yourself to start anything, however approach is everything. The style matters a lot. Approaching a woman infront of her mother is not very dj like, neither is approaching her infront of her man. Some people need to drop the "tough guy dj" attitude and learn technique and finesse. If you approach her the way Big Pappy describes "with her man, her mother" you will come off as a weird desperate fool. There's enough weirdo on this planet, you dont need to come off as one.
I feel this way. You have everything to gain and nothing to lose. Worst comes to worst, her man might come by and say "honey, who's this." That'll be your cue that she's probably taken

. If that happens, you've lost nothing. Perchance that she's actually single, then you can proceed.