Can a U visa be extended beyond the 4 years?
You asked if the U visa can be renewed beyond the 4 years – this may be possible in certain limited circumstances. (The law that addresses this is 8 CFR 214.14(g)(2)). To paraphrase, it states that U visa status can be extended in order to get a qualified family member into the US or if required by the law enforcement investigation (in which case the victim would need another law enforcement statement to get it extended).
You may want to talk to an attorney who specializes in U visas as soon as possible to find out whether you can adjust your status to legal permanent resident. As you can read here, it can be done after 3 years and before 4 years (when it expires):http://www.womenslaw.org/laws/federal/immigration/u-visa-laws-crime-vict…
Here are links for lawyers in STATE and some that are national organizations that you may want to contact to find one that specializes in U Visas:
LINK TO STATE LAWYERS and http://www.womenslaw.org/gethelp_national_type.php?type_id=1047