What should she do, and is she sinful if she cancels the contract and does not go, after her husband refused her going to work as a teacher on her first workday?

If the wife stipulated in the marriage contract that she would go out to work, then he [the husband] does not have the right to prevent her, unless the work is contrary to Islamic law or leads to the neglect of the household. However, if there was no such condition, then he has the right to prevent her from working as long as he provides for her adequately. There is no sin upon her for not going to work, because she is excused due to the lack of her husband's permission. The husband also has the right to annul any lease agreement his wife concluded without his permission. It is advisable for the spouses to communicate for the benefit of the family.