The Court of Federal Claims ruled against her. They cited several US cases including U.S. v. Darusamont. Therefore, the estate tax was due and payable. Congress has been given apparently ample authority to levy taxes retroactively. This was first decided in 1916 in Brushaber v. Union Pacific Railway Co. 240 US 1 (1916). In that case Congress passed the first income tax statute in October, 1913 (after the 16th Amendment was ratified). The tax was for the period March 1, 1913 through December 31, 1913. Union Pacific challenged the law including under the 5th Amendment and Due Process clauses of the Constitution. The Court rather summarily said that Congress had the power to retroactively tax. They have been pretty consistent about that ever since. See, U.S. v. Darusamont 449 US 292 (1981). Taxpayer had large capital gain and was retroactively hit with alternative minimum tax for 1976. The Income Tax case was a bit more dicey. The Court reviewed the file and determined that she should have received a deduction for estate taxes paid on the Fiduciary income tax return, but that again was permissible as the law was in effect before the end of the year and she knew what the rules were.