Tragic story but great reminder for us all to clean our dryer ducts.
In my last house, we had an appliance repair guy come out to see why our dryer was taking twice as long to dry a load of clothes. You guessed it - ductwork was full of lint, severely limiting air movement. We were lucky to get that wake-up call that way instead of via a fire.
I got a round brush on a long flexible rod, sort of like in the link above, but it doesn't attach to a drill - you just push it along and it loosens up the lint, and usually when you turn the dryer on it'll blow it out the end (I remove the louvered door first on the outside of the house).
Two things I've learned along the way, to prevent duct fires:
1. Never use plastic dryer vents
2. Don't use sheet metal screws to attach metal sections of dryer vent as they tend to snag lint as it passes by and lead to buildups.