If the IRS accepted your return you have to wait until it has been processed and then amend it. Meanwhile since you have put your Social Security number into the system, your sister will not be able to e-file her return this year, even if you amend. Your sister now has to print, sign and mail her own tax return that claims you as a dependent. She cannot e-file at all this year.
When your return has been fully processed you can use a Form 1040X to amend. That form is not available until the end of March, so post back then for help with amending.
**Disclaimer: Every effort has been made to offer the most correct information possible. The poster disclaims any legal responsibility for the accuracy of the information that is contained in this post.**
