Complex sentence: She completed the work by July 30,1926, when she wrote to enquire where she should send the designs for endorsement by the Commission of Fine Arts, tasked since 1921 with advising the Secretary of the Treasury on coinage design.
Split into simpler sentences: She completed the work by July 30,1926, when she wrote to enquire where she should send the designs for endorsement by the Commission of Fine Arts. This body since 1921 had been tasked with advising the Secretary of the Treasury on coinage design.