Anna Lanzilotti became stuck in her broken-down car in Matera, in the Basilicata region, when a wave of mud brought on by the rain hit, La Repubblica reported.
The 64-year-old was travelling with her daughter-in-law, who escaped unhurt and raised the alarm.
A police helicopter was brought out in an attempt to save Lanzilotti, with firefighters searching on the ground.
But after a two-hour search rescuers found the woman’s body a kilometre away.
Stormy weather has hit the country this week, bringing roaring thunder and heavy rain.
The shift follows soaring temperatures earlier this month which rose to over 40C, prompting warnings from the Ministry of Health.
The weather is due to be calmer over the coming days, although thunderstorms will hit again from Sunday, La Repubblica said.