Point your flashlight to Astrid and check your surroundings once in a while to check if The Blonde Vampire is there. If you can see her watching you or you see a hand coming closer from your right or left side, press SPACE bar to simply looking down.
Now if you want to play this minigame quick & easy, make sure to only do this quest after you progressed far enough with most quests done and have at least 1 million dollars ready to spend. Once you do, go to Tech Store and he will offer you 2 expensive yet better flashlights to buy.
Once you bought those, just do the quest and you can see that your flashlight is way brighter to the point you almost see the whole room and the Completion Bar below only takes a few seconds to complete.