Why did gitl slap hannah?

There lay little Tzipporah curled into a ball, her finger in her mouth like a stopper in a bottle. There is a fly on her cheek which Hannah reaches out to brush off until Gitl hoarsely demands, “Do not touch her!” When Hannah moves her hand forward again anyway, Gitl grabs her and slaps her twice. Then, she collapses and buries her face against Hannah’s shoulder, wondering aloud what she will tell Yitzchak. The little girl is dead.