Sgt. John Cummins with the sheriff's department said the woman, 75, was driving recklessly along I-20 mile marker 273, near Merkel.
"The woman appeared to be slightly confused, but not otherwise impaired," Cummins said in an email.
Vidaurri let her go.
Two hours later, he pulled over a different car near mile marker 277. While stopped on the side of the road, the same 75-year-old driver slammed into his vehicle from behind.
Both the deputy and the woman were injured and are being treated at Hendrick Medical Center.
The Department of Public Safety is investigating the crash.