Under the current rules, if you've entered the US illegally and were employed without UCIS authorization, you may not apply for adjustment of status in the US. (See section 10).

The amnesty provisions of Section 245(i) expired in 2001 and the DREAM Act - which would have allowed illegal aliens who were brought into the country as minors under the age of 16 to adjust their status - failed on a procedural vote in October of 2007.

You say your sister was born here. As a citizen, she may complete a family petition on your behalf when she reaches the age of 21 - but I think that it is required that you be outside the US when she does so.

As Aaron says, you should discuss this with a lawyer.