PA-28 Flight Instructor reported solo student made a long landing resulting in excessive braking and the aircraft leaving the runway striking a runway light and sign.

Narrative

Description of Incident:'During a supervised solo flight; the student pilot landed the aircraft past the halfway point of Runway XX; Upon realizing limited remaining runway distance; the student applied excessive braking in an attempt to stop the aircraft. This caused a loss of directional control; and the aircraft veered off the runway onto the grassy area beyond the end of the pavement. During the excursion; the aircraft struck a runway light and an airport sign. The student was uninjured.The flight instructor; who was present at the airport monitoring the solo flight; responded immediately to the scene to ensure the student's safety. After confirming the student was unharmed; the instructor manually moved the aircraft from the grass to a non-movement area and conducted a preliminary inspection for any visible damage. Following a thorough pre-flight inspection and confirming the aircraft was safe to taxi; the instructor returned the aircraft to the flight school and reported the incident to both the school manager and the chief pilot.Subsequently; the instructor and the chief pilot inspected the runway and taxiway for any debris or damage that could pose a hazard to other aircraft. The instructor also notified the airport manager and filed an incident report.