Walentynowicz was one of 96 people who died in the 2010 Polish Air Force Tu-154 crash near the city of Smolensk, Russia, Polskie Radio reported.
The exhumation of her body was called for by her family, who cited concerns over the accuracy of the Russian autopsies that followed the disaster.
Many people believe the crash, which also killed President Lech Kaczynski, his wife and other prominent Polish leaders, was not an accident, but an attack on the president.
If all goes according to plan, a second autopsy will be performed on Walentynowicz, which prominent Law and Justice party parliament member Antoni Macierewicz said may prove a bomb was aboard the flight.
Three other victims of the crash have been exhumed: two PiS MPs, Przemyslaw Gosiewski and Zbigniew Wassermann, and Janusz Kurtyka, the former head of the Institute of National Remembrance.
Donald Tusk, Poland's current prime minister, said imperfections in the Russian autopsies were not surprising.
"You know all too well what state the bodies were in after the crash," he told reporters at a press conference in March. "I should not comment on the determination of some families to exhume bodies, even if I do not understand this determination."