What is the test for filing an administrative claim under section 2401 of the Federal Tort Claims Act?

Section 2401(b) of the Federal Tort Claims Act requires that a plaintiff file an administrative claim with the appropriate federal agency "within two years after such claim accrues." 28 U.S.C. 2401(b). A claim accrues within the meaning of 2401(b) when the plaintiff knows, or in the exercise of reasonable diligence should have discovered, both the existence and the cause of her injury. United States v. Kubrick, 444 U.S. 111 (1979); Davis v. United States, 642 F.2d 328, 331 (9th Cir.1981), cert. denied, 455 U.S. 919 (1982).