If you included her 1099-DIV on your return instead of hers, you both need to amend. She will include it on her return and you will remove it from yours.
You can amend returns that have
been accepted by the IRS. If your return is pending, you won't be able to make any changes until it's accepted or rejected by the IRS. If you don't know your e-file status, we
can help you check it.
Select a tax year for specific
amending instructions.
Keep in mind: You have 3 years from the date you filed your return (or 2 years after you
paid the tax due, whichever is later) to file an amended return, which means
you don't have to get it done by the April 15 filing deadline.