Since you filed you own tax return the I will assume that you had more than $4,200 of taxable income which means that you cannot be a "Qualifying Relative" dependent.
To be a "Qualifying Child" dependent, you mist have lived for more than half the year in a home that your sister provided, or were away from that home temporarily to attend school.
If neither, then your sister cannot claim you and she must amend to remove you as a dependent. You can only paper file since your SSN has already been used and your e-file will reject.
**Disclaimer: This post is for discussion purposes only and is NOT tax advice. The author takes no responsibility for the accuracy of any information in this post.**
