Using last year's income and expenses as a guide, she'll estimate a new budget without her husband. She'll find that expenses will drop in some areas. Clothing, for instance. But many expenses will probably stay just about the same. Utilities, property taxes, and homeowner's insurance won't change much.
Housing is a critical expense.
She will need nearly as much living space as before. That may mean moving to a smaller or less desirable home. Some expenses will go up. Medical insurance is one potential problem. She could lose coverage through her husband's plan at work.