As vkou said, the hiring manager has no idea what taxes the wife will pay...but the payroll manager does, and could probably tell her exactly what she would pay

As vkou said, the hiring manager has no idea what taxes the wife will pay...but the payroll manager does, and could probably tell her exactly what she would pay based on her start date, estimated wages based on expected shifts, and exemptions. Expecting the hiring manager to know the tax stuff would be like expecting the dev team to know how much income tax the business is going to pay.