The website quotes Haniyeh's son Abdul Salam Haniyeh on Facebook sharing the news, saying that she suffered from "serious infections in the digestive tract that affected the nervous system."
She was first treated in the "Victory" hospital in Gaza, where Haniyeh visited her.
If I am understanding the article correctly, it may be too late. The girl is apparently in "clinical death" and Abdul said that the "skies were crying for her," a reference to recent rain.
(h/t Spotlighting)