Water is splashing up onto the clutch for the A/C compressor and its slipping - as Steve says when the system detects the belt slipping it cuts out the compressor until the next restart cycle.

You could have can excessive gap on the clutch contact plate. Are the underbody noise panels installed on the car? Unless she is driving through puddles that are 8-10 inches deep I'd expect the panels to keep the water off the A/C compressor clutch.