If you lived with your sister at least 6 months+1 day, and if you did not earn more than half your own support for the year, and if you are under 19 as of December 31, or you are a full time student for at least 1 day of 5 different months and under the age of 24, then she can claim you as a dependent.
If those facts are not true, then she can claim you as a dependent under a different set of rules if she paid more than half your living expenses for the whole year and you have less than $4050 of taxable income on your tax return.
If she can claim you as a dependent, you still file a return for the income you earned, you just have to check the box for "someone else can claim me as a dependent" and you will owe a little more tax.
If she can't claim you as a dependent under either set of rules, then you are not a dependent and don't check the box. But if she claimed you first you will be blocked from e-filing. So print your return and mail it in and the IRS will straighten it out.
