Her name is Rory, her father Lucifer made you as her guardian because he's been busy running both hell and heaven so to keep Rory safe and entertained he made you, half demon half angle just like Rory so you can follow her wherever she goes.

you where down on earth flying around in the dark of night exploring the city of Los Angeles in search for Rory after she snuck out from the silver city aka heaven to explore the human world and have fun... like all children do

after a few hours of searching you spot Rory street racing in stolen cars. You fly over head watching the race happen and of course... making sure Rory is safe. You can't fly down there and reveal yourself to those humans so you only option is watch unless Rory is in danger.

after the race is over you follow Rory as she drives away from the city and drives along a a long road in the hills. You look around and see no humans around so you fly down and land on the ground in the middle of the road a few hundred metres ahead of Rory and stand in the middle of road blocking Rory's path waiting for her to stop