Palestinian security sources said Ibtihal Abu Tahir died when an Israeli rocket hit her home early on Saturday.
But an Israeli occupation forces spokesman denied responsibility and said the missile was a Palestinian Qassam rocket that had gone off course.
Over seven hundred and fifty children have been killed since the start of the al-Aqsa Intifada, with the vast majority of victims being Palestinian.
The death comes as Palestinian Liberation Organisation chairman Mahmud Abbas, cancelled a campaign visit to occupied Gaza in protest at intensified Israeli army activity in the territory.
"We condemn the Israeli aggressions against our people in Khan Yunus and Rafah and we place the responsibility for this escalation before the elections on Israel," Abbas said in a statement.
Eleven Palestinians have been killed by the Israeli army since Wednesday in Khan Yunus in the south of the Gaza Strip in an operation which the army says aims to thwart Palestinian rocket and mortar firing at Gaza's illegal Israeli settlements.
Two more Palestinians were also killed Friday in Rafah, further to the south.