The victim, Yvonne Chua, died immediately, according to Director Nicanor Bartolome, chief of Manila police.
Bartolome said the package was delivered to the victim's house in the Manila suburban city of Taguig.
"There were three grenades inside the package and one exploded as the victim opened it," he said. "The victim was sitting on a sofa and the gift was on her lap when the blast occurred."
Chua's husband and 7-year-old son were not hurt in the explosion.
Bartolome said investigators were still determining who sent the package to the family.
