I don't think you shouldn't have been able to prepare your returns together at the same time last year (tax year 2016) because your spouse passed away during the tax year.
To transfer just your return forward, breaking it apart from your spouse's, select the option that you lived apart at the end of the year and that your marital status changed. Then, when you select Continue, TurboTax will give you the option to transfer your return apart from your spouse's.
