My thanks to Desmolicious and genji for your comments, much appreciated.
I knew as soon as I entered the room I had to capture the scene. The subject, light, colour and geometry were sublime, the circumstances less so. Very busy room, subject on mobile for 20 minutes whilst I tapped my foot impatiently. At no point was the subject aware that I was behind her. Eventually the planets aligned, everything came together and I got my shot.