Why does Rose Mary not want want to go to work in the morning?

Rose Mary didn't want to go to work the next morning because she hated her job.

Even though her students liked her, Mom hated teaching. She had to leave Maureen, who was not yet two, with a woman whose drug­dealer husband was serving time in the state prison. But what really bothered Mom was that her mother had been a teacher and had pushed Mom into getting a teaching degree so she would have a job to fall back on just in case her dreams of becoming an artist didn't pan out. Mom felt Grandma Smith had lacked faith in her artistic talent, and by becoming a teacher now, she was acknowledging that her mother had been right all along. At night she sulked and muttered under her breath. In the morning she slept late and pretended to be sick. It was up to Lori, Brian, and me to get her out of bed and see to it that she was dressed and at school on time.