Sylvia went on to serve as an assistant legal counsel in the Office of the U.S. Senate Legal Counsel. In that position, she represented Senate parties in litigation and advised Senate committees on legal matters related to investigations and other committee proceedings. She also spent 11 years as a San Francisco Deputy City Attorney, where she specialized in government ethics. 

In 2006, Sylvia became a partner at Phillips & Cohen LLP and has since become a leading expert in False Claims cases. Her book, The False Claims Act: Fraud Against the Government (with annual supplements), has served as an important reference for judges and attorneys in qui tam cases since it was first published in 2004. Because of her expertise in the False Claims Act and qui tam cases, Sylvia has consulted with state officials on ways to create and effectively expand state whistleblower laws.

Sylvia also regularly co-teaches a course on whistleblower law at Berkeley Law at the University of California. The class was one of the first courses on the False Claims Act and whistleblower laws taught at a major law school.