Final answer:
Under typical IRS rules, taxpayers have three years from the original filing date to file an amended tax return. For Valentina, who filed her 2019 tax return on April 15, 2020, the deadline to amend would be April 15, 2023.
Step-by-step explanation:
The subject of this question is related to the area of tax law, specifically the regulations governing the amendment of tax returns in the United States.
Under usual IRS rules, taxpayers have three years from the date they filed their original tax return to file an amended return if it was filed on or before the April 15th deadline. Valentina timely filed her 2019 tax return on April 15, 2020. Therefore, the last day she can generally file an amended 2019 tax return is April 15, 2023.
However, it's important to note that the exact date may vary if there are extensions granted or changes in tax law.