In the sub-section entitled “The Haircut,” why does Max choose Liesel to cut his hair?

Max chooses Liesel to cut his hair because she is the "calmest" of his choices.

He carried his own scissors and came forward, handing them not to Hans or Rosa but to the twelve-year-old girl. She was the calmest option. His mouth quivered a moment before he said, “Would you?”