Her alternator may not be supplying enough amps, causing the headlamps to be dim. I would have the alternator tested for amperage threshold.
〉 Answered on Feb 11th, 2008 by Amanda J. Pierce, MBA "AJ", Certified Mechanic, Project Coordinator; Primavera Scheduler at VIGOR Alaska Industrial Shipyard & BizzM3ch Solutions
You could have extra resistance in the circuit that robs some of the voltage for the bulbs. The first thing I would do would be to check how much voltage is actually getting to the bulbs. If this is low, I would check the connections to see if there's any corrosion or loose connections.
〉 Answered on Feb 11th, 2008 by Suzanne Grego, Technician at City of Philadelphia Fleet Management