After reading this answer I found out that the effects of Polyjuice potion persist even after a person dies. Generally, the transformation only lasts for one hour, but in the case of Barty Crouch's mother, she maintains her form for what could be assumed longer than that, since I doubt even Azkaban doesn't have some sort of service after a prisoner dies (i.e. notifying family, preparing the body for burial, having a ceremony, etc.).
“The Dementors are blind. They sensed one healthy, one dying person entering Azkaban. They sensed one healthy, one dying person leaving it. My father smuggled me out, disguised as my mother, in case any prisoners were watching through their doors. ‘My mother died a short while afterwards in Azkaban. She was careful to drink Polyjuice Potion until the end. She was buried under my name, and bearing my appearance. Everyone believed her to be me.”
- Harry Potter and the Goblet of Fire, Chapter 35 (Veritaserum)
While it also appears that the dosage a person drinks can alter how long the potion lasts, I find it unlikely that Barty's mom knew the exact time she was going to die and knew to drink a large portion of potion to cover any chance of it wearing off. So I'm left wondering how she could have maintained her son's appearance so long after her death.
So how long does a Polyjuice transformation last after death?