Eluana Englaro had been in a vegetative state since a car accident 17 years ago.
The Catholic church, which has opposed measures to let her die, implored God to "forgive" those responsible for Englaro's death.
"May the Lord welcome her and forgive those who led her there [to her death]," Javier Lozano Barragan, Vatican's health minister, told the ANSA news agency.
Al Jazeera's Sabina Castelfranco, reporting from Rome, said the reaction in Italy on Englaro's death was mixed.
"The country was completely divided between these who thought that after 17 years, she should be allowed to die, and these who felt that taking her off food and water would be wrong.
|Englaro's father fought for his daughters right to die [EPA]
"The Coliseum will remain lit all night tomorrow as a sign of deep mourning for Eluana."
Castelfranco said parliament will continue debating the issue on Tuesday and a vote on a new bill is expected to take place on Wednesday.
Silvio Berlusconi, the prime minister, had been trying to push a law through parliament that would forbid medics from withholding food and water to patients and effectively reverse the high court ruling that allowed Englaro to die.
The prime minister's supporters have a large majority in parliament and the bill is expected to pass.
Englaro's father accused Berlusconi of playing politics with his daughter's tragic situation.
"It was a coup de theatre. All I can say is that sometimes reality goes way beyond the wildest imagination," Beppino Englaro told Spain's El Pais newspaper on Sunday.
He also hit out at the Vatican for openly siding with the prime minister.
"The [Roman Catholic] church has nothing to do with this issue," Englaro said, adding that he felt the church should not "impose its values" on him.
Berlusconi had said that he would not allow the "killing" of Englaro and that the decision to stop feeding her amounts to euthanasia, which is illegal in Italy.
The issue also put the prime minister in conflict with Giorgio Napolitano, Italy's president, who on Friday refused to sign an emergency cabinet decree that would have prevented medics from removing Englaro's feeding tube.