Welcome to the Community, sarahdgt.
The Married, but withhold at higher single rate filing status option is unavailable in QuickBooks. However, Oregon uses the IRS's W-4. Thus, you can select Single instead to determine the income tax withheld from each employee's paycheck.
You can check this article for more details: W-4 Information for Employers.
Additionally, you can refer to the following article about setting up a new employee in your QuickBooks: New Payroll Setup Interview.
These resources should help to get you back on track. Drop me a comment below if you have any other questions about payroll. I'll be happy to help you further. Have a wonderful day.