I had a call a couple of years ago, they had 300 to 400 bees dead and dying on their driveway, followed their bodies to a tree with a hive in it same symptoms, I thought it could of been three things, IPV, poison, no food, I thought IPV was the most likely, eventually the hive died, hopefully the susceptibility to the virus is from the drone she is using now and not from the queen herself
good luck
Bob