What I might suggest for such a shot is to speed the shutter up to the flash-sync max speed. This will under expose the background, keeping the nice blur with a wider f-stop, and the flash will paint her in in such a way as to make her "pop" out of the composition. To do this you'll have to place the body in manual, the flash in TTL auto mode. Otherwise, the way you shot it is fine too. Nice composition.