How much longer I need to wait from my sister's I-130?

According to the June 2017 Visa Bulletin issued by the U.S. Department of State, visas are now available in the family-based F4 visa category (for siblings of U.S. citizens) for foreign nationals of most nationalities who have a Priority Date in 2004 or earlier. While that may appear to indicate approximately three more years until a visa is available and your sister could go forward with consular processing, in fact, priority dates progress and retrogress irregularly, and it could take significantly longer than three more years for a visa to become available. Some immigration law firms, including mine, offer legal services on a "flat fee" basis so that a client will know the total expense from the very beginning, and a few immigration law firms, including mine, offer an initial consultation free of charge.