Elrod was born in Port Arthur, Texas in 1966 and grew up in Baytown, Texas. She attended Baylor University from 1984-1988 and graduated magna cum laude with a B.A. degree in economics. She went to Harvard Law School in 1989 and received her J.D. in 1992, graduating cum laude. She became a member of the State Bar of Texas in 1992.
Elrod began her professional career by serving a two-year clerkship for federal district judge Sim Lake of the United States District Court for the Southern District of Texas. After completing her clerkship, she became an associate at the national law firm Baker Botts in 1994, where she practiced a wide variety of litigation matters for the next eight years.
In 2002, Governor Rick Perry appointed Elrod to be a judge on the 190th District Court in Harris County. She was elected to the judgeship in the 2002 general election, and again in 2006 when she ran unopposed. As a state district court judge, she presided over jury and bench trials involving civil litigation. Elrod remained on the Harris County bench until her confirmation to the Fifth Circuit.
President George W. Bush nominated Elrod to a vacancy on the Fifth Circuit on March 29, 2007 to replace Judge Patrick Higginbotham, who took Senior status on August 26, 2006. Elrod received a hearing before the Senate Judiciary Committee on July 19, 2007, and was voted out of committee on September 20, 2007. She was confirmed by the United States Senate by voice vote on October 4, 2007, just over six months after her nomination. Elrod was the fourth judge nominated to the Fifth Circuit by Bush and confirmed by the Senate. She maintains chambers in Houston, Texas. Her first published opinion for the Fifth Circuit, United States v. Spencer, was released on January 14, 2008.