Why does Mary decide to get a teaching job?

Dad said that if Mom wanted someone in the family to be punching a time clock, then she could get a job. She had a teaching degree, he pointed out.

Just after this comment, Rose Mary and Rex get into a huge fight, a physical fight, a fight that caused a crowd to gather in from of their building. The fight only ended because Rose Mary ended up dangling from the second story window, screaming that her husband was trying to kill her. The next morning, Rose Mary walked to the Intermediate School and got a job.