Question

Why did Madam Loisel run away in a hurry after a ball
was over?​

Answer 1

if you're asking why did she go back in a hurry, that was because she had lost her necklace

Answer 2

She left the ball early because after the ball she did not want people to see her impoverished conditions. Her husband did not have a personal vehicle; nor did they have proper elegant clothes to wear for the extreme cold outside. She did not want the rich people wearing elegant clothes to notice their modest and ordinary clothes. So, before the formal closing of the party she wanted to run away from the ball.