How did Zipporah stop God from killing Moses?

By cutting off her son's foreskin and throwing it at Moses's feet

And it came to pass by the way in the inn, that the LORD met him, and sought to kill him.

Then Zipporah took a sharp stone, and cut off the foreskin of her son, and cast it at his feet, and said, Surely a bloody husband art thou to me. Exodus 4:24-25