1/400th at F9, ISO 1600 (28mm).
The tough thing about taking shots like this is not the person you're taking the shot of. I had to get so close to fill the frame since I was using a 28mm lens, but if she had turned around I could have just smiled and showed her since it was a beautiful photo. The problem is being surrounded by 10 other people stopped at the streetlight wondering what the hell you're doing.
This is where confidence is important. It can be hard, but just try your best to ignore them, hold an air about you that you know what you're doing, and move on. It's a beautiful moment and photo to show if anyone asks what you're doing. And you should be proud of it.