10-year-old Maggy Mo'men who was injured in the Botroseya church bombing died of her injuries at Al-Galaa Military Hospital on Tuesday, bringing the death toll of the blast to 26.
Mo'men is a forth grade pupil at Ramses College school for girls. She received shrapnel in her brain and a lung laceration during the explosion and was lying in a coma at the hospital's intensive care unit.
Her condition was serious and she had been transferred from Al-Demerdash Hospital to the military hospital.
The funeral will be held at Botroseya church in Abbasiya at noon, sources said.
The militant group has also carried out deadly attacks in Cairo and has urged its supporters to launch attacks around the world in recent weeks as it goes on the defensive in its Iraqi and Syrian strongholds.
There was no immediate claim of responsibility, but exiled Brotherhood officials and home-grown militant groups condemned the attack. IS supporters celebrated on social media.
"God bless the person who did this blessed act," wrote one supporter on Telegram.
The explosion took place in a chapel, which adjoins St Mark's, Cairo's main cathedral and the seat of the Coptic Pope Tawadros II, where security is normally tight.